AP Physics 1 : Specific Forces

Study concepts, example questions & explanations for AP Physics 1

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Example Questions

Example Question #21 : Normal Force And Weight

A  box rests on a smooth table. An upward force of  is applied to the box so the box is lifted off the table. What is the upward acceleration of the box?  

Possible Answers:

Correct answer:

Explanation:

The correct answer is . There are 2 forces acting on the box: tension force () and normal force (). First we must calculate the force of the box:

 

The equation can be manipulated to solve for acceleration:

 

Example Question #22 : Normal Force And Weight

What is the weight of a car on Earth whose mass is ?

Possible Answers:

Correct answer:

Explanation:

Weight is the force that gravity exerts on an object. Weight is determined using the equation 

Where  is the mass of the object and  is the gravitational constant on the given planet.

On Earth, , so the weight of the car on Earth is:

Example Question #23 : Normal Force And Weight

What is the weight of a car on Mars whose mass is ? On Mars, .

Possible Answers:

Correct answer:

Explanation:

Weight is the force that gravity exerts on an object. Weight is determined using the equation 

Where  is the mass of the object and  is the gravitational constant on the given planet.

On Mars, , so the weight of the car on Mars is:

Example Question #24 : Normal Force And Weight

What is the normal force of a  block resting on a table?

Possible Answers:

Correct answer:

Explanation:

To begin solving our problem, we will create a free body diagram, labeling all our forces and the direction in which they are acting. 

Fbd 3

The normal force, , is the component of force perpendicular to the surface of contact. Weight, , is a force that gravity exerts on an object, acting in the same direction as gravity. To find the normal force, we will begin with Newton's 2nd law:

 

Where  is the sum of all forces in the same direction,  is mass, and  is the acceleration in the direction of the forces.

Since our object is at rest,  and Newton's 2nd law becomes:

 

Assuming  is in the positive direction, the sum of our forces in that direction is

Substituting in the definition of weight, , and solving the expression for  gives us 

Since  and 

Example Question #25 : Normal Force And Weight

What is the normal force of a  block resting on a table? 

Possible Answers:

Correct answer:

Explanation:

To begin solving our problem, we will create a free body diagram, labeling all our forces and the direction in which they are acting.

Fbd 3

The normal force, , is the component of force perpendicular to the surface of contact. Weight, , is a force that gravity exerts on an object, acting in the same direction as gravity.

To find the normal force, we will begin with Newton's 2nd law:

 

Where  is the sum of all forces in the same direction,  is mass, and  is the acceleration in the direction of the forces.

Since our object is at rest,  and Newton's 2nd law becomes

 

Assuming  is in the positive direction, the sum of our forces in that direction is

Substituting in the definition of weight, , and solving the expression for  gives us 

Since  and 

Example Question #26 : Normal Force And Weight

What is the normal force of a  block resting on a ramp, ?

Possible Answers:

Correct answer:

Explanation:

To begin solving our problem, we will create a free body diagram, labeling all our forces and the direction in which they are acting. 

Inclined ramp fbd

The normal force, , is the component of force perpendicular to the surface of contact. Weight, , is a force that gravity exerts on an object, acting in the same direction as gravity.

Weight must be divided into two components, the parts acting parallel and perpendicular to the contact surface.

Inclined ramp resolved fbd  1

 is the x-component of the weight and is 

 is the y-component of the weight and is 

To find the normal force, we will begin with Newton's 2nd law:

 

Where  is the sum of all forces in the same direction,  is mass, and  is the acceleration in the direction of the forces.

Since our object is at rest,  and Newton's 2nd law becomes

 

To find , we only need to consider forces acting the same or opposite direction as .

Assuming  is in the positive direction, the sum of our forces in that direction is

Substituting in  , and solving the expression for  gives us 

Since  and 

Example Question #27 : Normal Force And Weight

What is the normal force of a  block resting on a ramp, ?

Possible Answers:

Correct answer:

Explanation:

To begin solving our problem, we will create a free body diagram, labeling all our forces and the direction in which they are acting.

Inclined ramp fbd

The normal force, , is the component of force perpendicular to the surface of contact. Weight, , is a force that gravity exerts on an object, acting in the same direction as gravity.

Weight must be divided into two components, the parts acting parallel and perpendicular to the contact surface.

Inclined ramp resolved fbd  1

 is the x-component of the weight and is 

 is the y-component of the weight and is 

To find the normal force, we will begin with Newton's 2nd law:

 

Where  is the sum of all forces in the same direction,  is mass, and  is the acceleration in the direction of the forces.

Since our object is at rest,  and Newton's 2nd law becomes

 

To find , we only need to consider forces acting the same or opposite direction as .

Assuming  is in the positive direction, the sum of our forces is

Substituting in  , and solving the expression for  gives us 

Since  and 

Example Question #28 : Normal Force And Weight

What is the normal force acting on a  book with  pressing down on it?

Possible Answers:

Correct answer:

Explanation:

To begin solving our problem, we will create a free body diagram, labeling all our forces and the direction in which they are acting.

Fbd force down

The normal force, , is the component of force perpendicular to the surface of contact. Weight, , is a force that gravity exerts on an object, acting in the same direction as gravity.  is the force pressing down on the book.

To find the normal force, we will begin with Newton's 2nd law:

 

Where  is the sum of all forces in the same direction,  is mass, and  is the acceleration in the direction of the forces.

Since our object is at rest,  and Newton's 2nd law becomes

 

Assuming  is in the positive direction, the sum of our forces in that direction is

Substituting in the definition of weight, , and solving the expression for  gives us 

Since ,   and 

Example Question #29 : Normal Force And Weight

What is the normal force acting on a  television with  pulling up on it?

Possible Answers:

Correct answer:

Explanation:

To begin solving our problem, we will create a free body diagram, labeling all our forces and the direction in which they are acting.

Fbd force up

The normal force, , is the component of force perpendicular to the surface of contact. Weight, , is a force that gravity exerts on an object, acting in the same direction as gravity.   is the force pulling up on the book.

To find the normal force, we will begin with Newton's 2nd law:

 

Where  is the sum of all forces in the same direction,  is mass, and  is the acceleration in the direction of the forces.

Since our object is at rest,  and Newton's 2nd law becomes

 

Assuming  is in the positive direction, the sum of our forces acting in that direction is

Substituting in the definition of weight, , and solving the expression for  gives us 

Since ,  and 

Example Question #30 : Normal Force And Weight

What is the mass of a  plane?

Possible Answers:

Correct answer:

Explanation:

Weight is the force that gravity exerts on an object. Weight is determined using the equation  where  is the mass of the object and  is the gravitational constant on the given planet.

Given the weight of an object and the gravitational constant acting on it, we find the mass using

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