Forces - High School Physics
Card 0 of 20
Jerry pushes a 
box with 
of force. What is the resultant acceleration?
Jerry pushes a
Newton's second law states that 
.
In this problem, 
and 
.
Plug these into the equation to solve for acceleration.
Newton's second law states that
In this problem,
Plug these into the equation to solve for acceleration.
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A 
ball rolls forward with a net acceleration of 
. What is the net force on the ball?
A
Newton's second law states that 
.
Plug in the values given to us and solve for the force.
Newton's second law states that
Plug in the values given to us and solve for the force.
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Louisa rolls a ball with 
of force. She observes that it has a constant linear acceleration of 
. What is the mass of the ball?
Louisa rolls a ball with
Newton's second law states that 
.
Plug in the given values to solve for the mass.
Newton's second law states that
Plug in the given values to solve for the mass.
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Derek pushes a 
crate along a rough surface with 
of force. He observes that it is only accelerating at a rate of 
. What must the value of the force of friction be?
(Assume the only two forces acting on the object are friction and Derek).
Derek pushes a
(Assume the only two forces acting on the object are friction and Derek).
Newton's second law states that 
.
If Derek is pushing with 
of force, then we should be able to solve for the acceleration of the 
crate.
Derek observes that the crate is acceleration at a rate of 
, rather than the expected 
. An outside force is acting upon it to slow the acceleration.
The equation for the net force on the object is: 
. We also know, from Newton's second law, that 
, where the resultant force and acceleration are the values actually observed.
Plug in the information we've been given so far to find the force of friction.
Subtract 
from both sides to find the force of friction.
Friction will be negative because it acts in the direction opposite to the force of Derek.
Newton's second law states that
If Derek is pushing with
Derek observes that the crate is acceleration at a rate of
The equation for the net force on the object is:
Plug in the information we've been given so far to find the force of friction.
Subtract
Friction will be negative because it acts in the direction opposite to the force of Derek.
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A hammer exerts a 
force on a nail. What is the force the nail exerts on the hammer?
A hammer exerts a
Newton's third law states that when one object exerts a force on a second object, the second object exerts a force equal in size, but opposite in direction to the first. That means that the force of the hammer on the nail and the nail on the hammer will be equal in size, but opposite in direction.
Since the hammer exerts 
of force on the nail, the nail must exert 
of force on the hammer.
Newton's third law states that when one object exerts a force on a second object, the second object exerts a force equal in size, but opposite in direction to the first. That means that the force of the hammer on the nail and the nail on the hammer will be equal in size, but opposite in direction.
Since the hammer exerts
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Michael pushes a 
box with 
of force to the left. Annie pushes the same box with 
of force to the right. What is the net force on the box?
Michael pushes a
For the net force, we add up all the forces: 
.
Since force is a vector, the direction of the action matters. We will make leftward motion negative and rightward motion positive. Michael is pushing with 
to the left, making his force equal to 
. Annie was pushing with 
to the right, so her force will remain 
.
We can find the net force by adding the individual force together.
For the net force, we add up all the forces:
Since force is a vector, the direction of the action matters. We will make leftward motion negative and rightward motion positive. Michael is pushing with
We can find the net force by adding the individual force together.
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Franklin lifts a 
weight vertically. If he lifts it so that way the velocity of the weight is constant, how much force is he using?
Franklin lifts a
If the object has a constant velocity, that means that the net acceleration must be zero.
In conjunction with Newton's second law, we can see that the net force is also zero. If there is no net acceleration, then there is no net force.
Since Franklin is lifting the weight vertically, that means there will be two force acting upon the weight: his lifting force and gravity. The net force will be equal to the sum of the forces acting on the weight.
Since we just proved that the net force will equal zero, we can say 
.
We know the mass of the weight and we know the acceleration, so we can solve for the lifting force.
If the object has a constant velocity, that means that the net acceleration must be zero.
In conjunction with Newton's second law, we can see that the net force is also zero. If there is no net acceleration, then there is no net force.
Since Franklin is lifting the weight vertically, that means there will be two force acting upon the weight: his lifting force and gravity. The net force will be equal to the sum of the forces acting on the weight.
Since we just proved that the net force will equal zero, we can say
We know the mass of the weight and we know the acceleration, so we can solve for the lifting force.
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A 
box starts at rest and reaches a velocity of 
after traveling a distance 
. What was the force on the box?
A
The formula for force is 
.
We are given the mass, but we will need to calculate the acceleration to use in the formula.
We know the initial velocity (zero because the box starts from rest), final velocity, and distance traveled. Using these values, we can find the acceleration using the formula 
.
Plug in our given values and solve for acceleration.
Divide both sides by 
.
Now we know both the acceleration and the mass, allowing us to solve for the force.
The formula for force is
We are given the mass, but we will need to calculate the acceleration to use in the formula.
We know the initial velocity (zero because the box starts from rest), final velocity, and distance traveled. Using these values, we can find the acceleration using the formula
Plug in our given values and solve for acceleration.
Divide both sides by
Now we know both the acceleration and the mass, allowing us to solve for the force.
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An airplane has a mass of 
. What is the minimum necessary lift force to get the airplane off the ground?
An airplane has a mass of
In this problem there will be two forces acting upon the airplane: the weight of the plane (force of gravity) and the lifting force. Since we are looking for the minimum force to lift the plane, we can set the two forces equal to each other: 
.
We can calculate the gravitational force using the mass.
Returning to the original equation, we see that the lifting force must be 
.
In this problem there will be two forces acting upon the airplane: the weight of the plane (force of gravity) and the lifting force. Since we are looking for the minimum force to lift the plane, we can set the two forces equal to each other:
We can calculate the gravitational force using the mass.
Returning to the original equation, we see that the lifting force must be
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A dog bites down on a chew toy with 
of force. What is the force of the chew toy on the dog?
A dog bites down on a chew toy with
Use Newton's third law to solve this question. The force of the dog on the chew toy is equal in magnitude, but opposite of direction, to the force of the chew toy acting on the dog.
That means that 
.
Using our given values for find the force of the chew toy.
Use Newton's third law to solve this question. The force of the dog on the chew toy is equal in magnitude, but opposite of direction, to the force of the chew toy acting on the dog.
That means that
Using our given values for find the force of the chew toy.
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If the mass of the object is 
and 
, what is the normal force on the object?
If the mass of the object is
The normal force is always perpendicular to the surface upon which the object is moving, and is pointed away from said surface. That means we are looking for the value for Z in the diagram.
Observe that Z and Y are equal, but opposite forces.
If we can solve for Y, then we can find Z.
We can use our understanding of trigonometry to find an equation for Y.
If we plug in 
for the angle, we see:
Since we are solving for Y, we can multiply both sides by W.
Now that we know an equation for Y, we can return to our original equation to solve for Z.
From here, we can use Newton's second law to find the value of W, the total force of gravity.
Substitute this into our equation for Z.
Now we can solve for Z using the values given in the question for the angle, mass, and gravity.
The normal force is always perpendicular to the surface upon which the object is moving, and is pointed away from said surface. That means we are looking for the value for Z in the diagram.
Observe that Z and Y are equal, but opposite forces.
If we can solve for Y, then we can find Z.
We can use our understanding of trigonometry to find an equation for Y.
If we plug in
Since we are solving for Y, we can multiply both sides by W.
Now that we know an equation for Y, we can return to our original equation to solve for Z.
From here, we can use Newton's second law to find the value of W, the total force of gravity.
Substitute this into our equation for Z.
Now we can solve for Z using the values given in the question for the angle, mass, and gravity.
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If the mass of the object is 
and 
, what is the normal force on the object?
If the mass of the object is
The normal force is always perpendicular to the surface upon which the object is moving, and is pointed away from said surface. That means we are looking for the value for Z in the diagram.
Observe that Z and Y are equal, but opposite forces.
If we can solve for Y, then we can find Z.
We can use our understanding of trigonometry to find an equation for Y.
If we plug in 
for the angle, we see:
Since we are solving for Y, we can multiply both sides by W.
Now that we know an equation for Y, we can return to our original equation to solve for Z.
From here, we can use Newton's second law to find the value of W, the total force of gravity.
Substitute this into our equation for Z.
Now we can solve for Z using the values given in the question for the angle, mass, and gravity.
The normal force is always perpendicular to the surface upon which the object is moving, and is pointed away from said surface. That means we are looking for the value for Z in the diagram.
Observe that Z and Y are equal, but opposite forces.
If we can solve for Y, then we can find Z.
We can use our understanding of trigonometry to find an equation for Y.
If we plug in
Since we are solving for Y, we can multiply both sides by W.
Now that we know an equation for Y, we can return to our original equation to solve for Z.
From here, we can use Newton's second law to find the value of W, the total force of gravity.
Substitute this into our equation for Z.
Now we can solve for Z using the values given in the question for the angle, mass, and gravity.
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How much force is required to acclerate a 
crate at 
?
How much force is required to acclerate a
The formula for force is 
. Plug in our given values and solve:
The formula for force is
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Miguel pushes a box with 
of force to the left. His sister Alexis pushes with 
of force to the right. What is the net force on the box?
Miguel pushes a box with
We need to look at the net force, which is the sum of the other forces:
Since Alexis and Miguel are pushing with the same value but in opposite directions, make one of these forces negative:
Therefore, the net force upon the object is 
.
We need to look at the net force, which is the sum of the other forces:
Since Alexis and Miguel are pushing with the same value but in opposite directions, make one of these forces negative:
Therefore, the net force upon the object is
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The force acting upon a crate is 
. If the mass of the crate is 
, what is the acceleration?
The force acting upon a crate is
For this problem use Newton's second law:
We are given the total force and the mass, allowing us to solve for the acceleration.
For this problem use Newton's second law:
We are given the total force and the mass, allowing us to solve for the acceleration.
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Two dogs pull on a bone. One pulls with 
of force to the right and one pulls with 
of force to the left. What is the net force on the bone?
Two dogs pull on a bone. One pulls with
Force is a vector quantity, meaning that both magnitude and direction are important factors. Net force is calculated by summing all of the forces acting on an object.
For this question, we will assign "to the right" as the positive direction and "to the left" as the negative direction. Under these conditions, we can add the given forces to find the net force.
This means that it has a net force of 
to the left.
Force is a vector quantity, meaning that both magnitude and direction are important factors. Net force is calculated by summing all of the forces acting on an object.
For this question, we will assign "to the right" as the positive direction and "to the left" as the negative direction. Under these conditions, we can add the given forces to find the net force.
This means that it has a net force of
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A block is on a smooth horizontal surface (
), connected by a tine cord that passes over a pulley to a second block which hangs vertically (
). Find the formula for the acceleration of the system. Ignore friction and the masses of the pulley and cord.
A block is on a smooth horizontal surface (
To determine the net force on a system, it is important to consider all the forces between each object in the same direction. The direction to be considered is along the line of the rope. The system is considered to be all the blocks together as they will all move with the same acceleration.
According to Newton’s 3rd Law, the Tension in the rope caused by A pulling on B and B pulling on A is equal in magnitude and opposite in direction. Therefore these two Tension forces cancel out.
From Newton’s 2nd law we know that the net force on a system is equal to the mass of the system times the acceleration of the system
Therefore
We can calculate the force of gravity from the equation Fg = mg
Therefore
We can rearrange this equation and solve for a
To determine the net force on a system, it is important to consider all the forces between each object in the same direction. The direction to be considered is along the line of the rope. The system is considered to be all the blocks together as they will all move with the same acceleration.
According to Newton’s 3rd Law, the Tension in the rope caused by A pulling on B and B pulling on A is equal in magnitude and opposite in direction. Therefore these two Tension forces cancel out.
From Newton’s 2nd law we know that the net force on a system is equal to the mass of the system times the acceleration of the system
Therefore
We can calculate the force of gravity from the equation Fg = mg
Therefore
We can rearrange this equation and solve for a
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Three blocks on a frictionless horizontal surface as in contact with each other. A force is applied to the first block (
). Determine the net force on block B terms of 
, 
, and 
and 
.
Three blocks on a frictionless horizontal surface as in contact with each other. A force is applied to the first block (
To determine the net force on a system, it is important to consider all the forces between each object in the horizontal direction. The system is considered to be all the blocks together as they will all move with the same acceleration.
According to Newton’s 3rd Law 
and 
are equal in magnitude and opposite in direction so they will cancel out. The same goes for 
and 
.
Therefore our equation is reduce to
From Newton’s 2nd law we know that the net force on a system is equal to the mass of the system times the acceleration of the system
Therefore
This means that the acceleration on any one block is
So when solving for the net force on any one block, the net force on the single block will be equal to that block's mass times the acceleration of the system. Therefore for block B, the net force is
To determine the net force on a system, it is important to consider all the forces between each object in the horizontal direction. The system is considered to be all the blocks together as they will all move with the same acceleration.
According to Newton’s 3rd Law 
Therefore our equation is reduce to
From Newton’s 2nd law we know that the net force on a system is equal to the mass of the system times the acceleration of the system
Therefore
This means that the acceleration on any one block is
So when solving for the net force on any one block, the net force on the single block will be equal to that block's mass times the acceleration of the system. Therefore for block B, the net force is
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A child slides down a slide with a 30 degree incline, and at the bottom her speed is precisely half what it would have been if the slide had been frictionless. Calculate the coefficient of kinetic friction between the slide and the child.
A child slides down a slide with a 30 degree incline, and at the bottom her speed is precisely half what it would have been if the slide had been frictionless. Calculate the coefficient of kinetic friction between the slide and the child.
Consider the net forces acting on the object causing it to accelerate.
To determine the Force of Gravity in the x-direction, we must break the force of gravity into components and examine the side acting in the x-direction. Using trigonometric functions we get that
We know that the force of gravity is equal to mg
According to Newton’s 2nd law the force is equal to the mass times the acceleration of the object.
The force of friction is directly related to 
(the coefficient of friction) times the normal force. In this case the normal force is equal to the y component of the force of gravity.
Therefore
If we substitute this in our original net force equation
Notice that mass is in each piece of the equation so we can cancel it out.
We can also use our kinematic equations to determine the speed of the object at the bottom of the incline. We can represent 
to be the length of the slope.
Since the ball is assumed to be at rest at the top of the incline, the initial velocity at the top will be 0.
Therefore
Solving for 
on its own we get
In the original situation, the force of gravity is the only force pulling on the object. Therefore the acceleration is
We can substitute this value into our velocity equation
In the second situation the velocity is one half of the original velocity. Therefore
We can place this back into our kinematic equation and rearrange it to solve for the acceleration.
We can then substitute that into our net force acceleration equation
Notice that g is in all of these terms so we can cancel it out.
Now we can substitute and solve
Consider the net forces acting on the object causing it to accelerate.
To determine the Force of Gravity in the x-direction, we must break the force of gravity into components and examine the side acting in the x-direction. Using trigonometric functions we get that
We know that the force of gravity is equal to mg
According to Newton’s 2nd law the force is equal to the mass times the acceleration of the object.
The force of friction is directly related to 
Therefore
If we substitute this in our original net force equation
Notice that mass is in each piece of the equation so we can cancel it out.
We can also use our kinematic equations to determine the speed of the object at the bottom of the incline. We can represent 
Since the ball is assumed to be at rest at the top of the incline, the initial velocity at the top will be 0.
Therefore
Solving for 
In the original situation, the force of gravity is the only force pulling on the object. Therefore the acceleration is
We can substitute this value into our velocity equation
In the second situation the velocity is one half of the original velocity. Therefore
We can place this back into our kinematic equation and rearrange it to solve for the acceleration.
We can then substitute that into our net force acceleration equation
Notice that g is in all of these terms so we can cancel it out.
Now we can substitute and solve
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Susan is trying to push a 
crate across the floor. She observes that the force of friction between the crate and the floor is 
. What is the coefficient of static friction? Assume 
Susan is trying to push a 
The equation for the force of friction is 
, where μ is the coefficient of static friction.
The normal force is equal to the mass times acceleration due to gravity, but in the opposite direction (negative of the force of gravity).
Since the problem tells us that the force due to friction is 
, we can plug these values into our original equation to solve for the coefficient of friction.
The coefficient of friction has no units.
The equation for the force of friction is 
The normal force is equal to the mass times acceleration due to gravity, but in the opposite direction (negative of the force of gravity).
Since the problem tells us that the force due to friction is 
The coefficient of friction has no units.
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