Question

A car is going up a hill. While doing so, its speed is decreasing. What forms of energy does it have? Select all forms that are present. (It's gas tank is not empty).

A) kinetic energy
B) chemical potential energy
C) thermal energy
D) gravitational potential energy

2.

For the same car, while going up the hill with decreasing speed, which forms of energy are increasing in amount?

A) kinetic energy
B) chemical potential energy
C) gravitational potential energy
D) thermal energy

3.

Which of the following are examples of work, using the definition of work used in physics?

A) work done on a wall by pushing the wall with a large force without moving it
B) work done by the normal force as a book slides along a horizontal table
C) work done on a heavy box as you carry it across the room at the same height at constant speed
D) work done on a heavy barbell while holding it still above your head
E) work done on a thumbtack as you push it into a bulletin board

4.

Whenever work is done on an object, what will always be true?

A) heat is produced
B) the speed of the object will change
C) the gravitational potential energy of the object will change
D) the height of the object will change
E) the energy of the object will change

5.

While a book slides across a horizontal table and comes to a stop which force(s) do(es) work? (Select all forces that do work on the book).

A) the weight of the book
B) the kinetic friction of the table on the book
C) the normal force of the table on the book

6.

While a lawn mower moves forward 2 meters, a man pulls on the handle of the lawnmower with a force of 100 Newtons. The angle between the displacement of the lawn mower and the direction of the applied force is 135.6 degrees. How much work was done on the lawnmower by the man?

A) 200 Joules
B) - 200 Joules
C) zero
D) - 141 Joules
E) 141 Joules

7.

If the lawn-mower had 300 Joules of kinetic energy before the man pulled on it, about how much kinetic energy does it have after the work done by the man? (Assume there are no energy losses to friction).

A) 440 Joules
B) 500 Joules
C) 300 Joules
D) negative kinetic energy
E) 160 Joules

8.

A car changes its speed from 30 mph to 90 mph. How many times greater is its final kinetic energy compared to its initial kinetic energy?

A) eight times as much
B) four times as much
C) twice as much
D) three times as much
E) nine times as much

9.

Assume that the car changes chemical potential energy (gasoline) into kinetic energy with the same efficiency at all speeds. How many times more gas will it take far the car to go from 30 to 90 mph, compared to going from zero to 30 mph?

A) twice as much
B) nine times as much
C) three times as much
D) six times as much
E) the same amount
F) eight times as much

10.

The scalar product of two vectors is equal to ...(choose all correct responses).

A) the magnitude of the first vector times the magnitude of the second vector times the cosine of the angle between the vectors
B) the magnitude of one of the vectors multiplied by the component of the other vector that is parallel to the first vector
C) a vector quantity
D) the product of a scalar and a vector
E) none of the other answers is correct

Answer 1

(1) Option (A) and (D)

Explanation -

As the car's speed is decreasing, it still has kinetic energy. While going upside of hill the car gains gravitational potential energy.

(2) (C) Gravitational potential energy.

Explanation -

While going upside the hill, it height above the ground level increases so it gains gravitational potential energy.

(3) Option (C)

Explanation -

The work is said to be done, if there is displacement in the direction of application of force.

In option (C) only, there is displacement in the direction of force. So work is said to be done.

(4) All the options, (A), (B), (C), (D) and (E) are correct options.

Explanation -

When work is done, heat may be produced, gravitational energy may change, speed may change and energy of the body may change.

(5) Option (B) is the correct answer.

Only kinetic friction will do the work.

Work done by weight of book and normal force will be zero.

Because, W = F*s*cos

And in option (A) and (C), = 90 deg

So, cos = cos90 = 0

So, work done W = 0