Review for Energy Exam

What is the work required for 60 kg astronaut to lift herself

0.2 m on Earth

0.2 m

Ans. 120 J

What is the work required for a 60 kg astronaut to lift herself

0.2 m on Planet X? (g = 2 m/s2)

0.2 m

Ans. 24 J

What is the PEg of a 20,000 kg lunar lander that is 100 m

above the surface of the Moon?

(g = 2 m/s2)

100 mAns. 4,000,000 J

What is the KE at point C?

h

½ hPE = 0

PE KE

20 J

A

B

C

D

Ans. 10 J

What is the speed of the 1 kg ball at point C?

h

½ hPE = 0

PE KE

20 J

A

B

C

D

Ans. 4.5 m/s

The car at B has _____ times as much KE as it had at A

20 m/s 40 m/s 60 m/s

A B C

Ans. 4

The car at C has _____ as much KE as it had at A

20 m/s 40 m/s 60 m/s

A B C

Ans. 9

What is the primary form of energy present in this situation?

Ans. PEs

What form(s) of energy are present in this

situation?

Ans. PEs, PEg

What was the work done on the 1000 kg car?

5 m/s 25 m/s

Before After

Ans. 300,000 J

A 5 kg lead ball and a 2 kg

wooden ball are dropped from

the same height. Which has more

PEg?Ans. Lead ball

A 5 kg lead ball and a 2 kg

wooden ball are dropped from the

same height. How do their KEs compare before

striking the ground? Ignore air resistance.

Ans. Lead KE is greater

A 5 kg lead ball and a 2 kg

wooden ball are dropped from the

same height. How do their

speeds compare before striking the ground? Ignore air resistance.

Ans. Speeds same

The motion of a 2 kg cart is shown below. What is its KE

at t = 6 s?

0

30

60

0 1 2 3 4 5 6 7 8 9 10

11

12

13

14

15

16

17

18

19

20

Time (sec)

Velocity (m/s)

Ans. 900 J

If Sally and Sam have the same mass, which one has the greater

KE?

00

position

time

SamSally

Ans. Sally

What forms of energy does the baseball have?

Ans. KE, PEg

What is the stiffness (k) of this spring?

0

30

60

0 1 2 3 4 5 6 7 8 9 10

11

12

13

14

15

16

17

18

19

20

Stretch (m)

Force (N)

Ans. 6 N/m

What is the PEs when the spring is stretched to 5 m?

0

30

60

0 1 2 3 4 5 6 7 8 9 10

11

12

13

14

15

16

17

18

19

20

Stretch (m)

Force (N)

Ans. 75 J

If all of the PEchem of a typical doughnut could

be used to do work, how high could a 50 kg

person climb?

PEchem = 1,000,000 J

?Ans. 2 km

A skier has a choice of the following two frictionless slopes. Along which slope will he end up with the greatest

speed at the bottom?

Slope A Slope B

Ans. Same speed

A diver falling from 2h will have _____ as much KE hitting the water as a diver

falling from h

Ans. twice

A diver falling from 4h will have _____ as much speed hitting the water as a diver

falling from h

Ans. twice

A 20 kg kid starts from rest at point A. What is his PEg at A?

6 m

3 m

A

B

C

Ans. 1200 J

What is the 20 kg kid’s PEg at point C?

6 m

3 m

A

B

C

Ans. 600 J

What is the 20 kg kid’s KE at point B?

6 m

3 m

A

B

C

Ans. 1200 J

What is the 20 kg kid’s KE at point C?

6 m

3 m

A

B

C

Ans. 600 J

What is the 20 kg kid’s speed at point B?

6 m

3 m

A

B

C

Ans. 11 m/s

What is the work done on the dog? Into what form of energy

does this work go?

Dog slides 2 m

30 N

Dog is motionless at end

Ans. 60 J; thermal

After hitting a 0.4 kg soccer ball with her head, it travels 6 m straight up.

What was the work she did on

the ball?

6 m

Ans. 24 J