Question 1

Which of the following best defines gravitational potential energy for an object of mass $$m at $$height $$y$$ above the ground?

Accepted Answer

$$U_{grav} = mgy$$

Question 2

A 2 kg object is lifted from a height of 1 m to 5 m above the ground. What is the change in its gravitational potential energy? (Take $$g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$\Delta U_{grav} = 78.4 \ \mathrm{J}$$

Question 3

Which equation correctly expresses the work done by gravity when an object moves from an initial height $$y_o to a $$final height $$y_f$$?

Accepted Answer

$$W_{grav} = mgy_o - mgy_f$$

Question 4

If an object is dropped from a height $$y_o$$ and lands at $$y_f = 0$$, what is the work done by gravity?

Accepted Answer

$$W_{grav} = mgy_o$$

Question 5

Which of the following statements is true about gravitational potential energy?

Accepted Answer

It depends on the mass, gravitational acceleration, and height above a reference point.

Question 6

A student lifts a 5 kg box from the floor ($$y=0) to a $$shelf at $$y=2 m. $$What is the gravitational potential energy of the box on the shelf? ($$g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$U_{grav} = 98 \ \mathrm{J}$$

Question 7

Which formula represents the relationship between the initial and final gravitational potential energies and the work done by gravity?

Accepted Answer

$$W_{grav} = U_o - U_f$$

Question 8

A hiker lifts a 10 kg backpack from the ground to a ledge 3 m high. What is the work done by gravity during this process?

Accepted Answer

$$W_{grav} = -294 \ \mathrm{J}$$

Question 9

If the reference point for gravitational potential energy is changed from the ground to the top of a building, how does the value of $$U_{grav}$$ for an object at ground level change?

Accepted Answer

It becomes negative.

Question 10

A ball of mass 0.5 kg is thrown vertically upward from ground level to a maximum height of 4 m. What is its gravitational potential energy at the top? ($$g = 9.8 \ \mathrm{m/s^2$})$$

Accepted Answer

$$U_{grav} = 19.6 \ \mathrm{J}$$

Question 11

Which of the following scenarios involves a decrease in gravitational potential energy?

Accepted Answer

A rock falls from a cliff to the ground.

Question 12

If $$U_o = 50 \ \mathrm{J}$$ and $$U_f = 20 \ \mathrm{J}$$, what is the work done by gravity?

Accepted Answer

$$W_{grav} = 30 \ \mathrm{J}$$

Question 13

A 3 kg object is moved from $$y_o = 2 m to$$ $$y_f = 6 m. $$What is the work done by gravity?

Accepted Answer

$$W_{grav} = -117.6 \ \mathrm{J}$$

Question 14

Which of the following is NOT a factor in calculating gravitational potential energy?

Accepted Answer

The velocity of the object.

Question 15

A construction worker lifts a 20 kg beam from $$y_o = 0 m to$$ $$y_f = 10 m. $$What is the change in gravitational potential energy?

Accepted Answer

$$\Delta U_{grav} = 1960 \ \mathrm{J}$$

Question 16

Which equation would you use to find the gravitational potential energy lost by an object falling from height $$y_o to$$ $$y_f$$?

Accepted Answer

$$U_{grav, lost} = mgy_o - mgy_f$$

Question 17

A 1.5 kg object is dropped from a height of 8 m. What is its gravitational potential energy just before it hits the ground?

Accepted Answer

$$U_{grav} = 117.6 \ \mathrm{J}$$

Question 18

If the gravitational potential energy of an object is zero at ground level, what is its potential energy at a height $$h$$?

Accepted Answer

$$U_{grav} = mgh$$

Question 19

A climber of mass 70 kg ascends from $$y_o = 100 m to$$ $$y_f = 250 m. $$What is the work done by gravity?

Accepted Answer

$$W_{grav} = -10,290 \ \mathrm{J}$$

Gravitational Potential Energy and Work in Physics

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