# AP Physics 1 : Specific Forces

## 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?

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 ?

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, .

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?

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.

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?

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.

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, ?

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.

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.

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, ?

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.

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.

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?

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.

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?

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.

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?