brodidit for students
Work, energy and power
MDCAT · Physics · 6 questions
Name: ____________________ Date: ____________
A force of 10 N pushes a box 5 m in the direction of the force. How much work is done?
- A 2 J
- B 15 J
- C 500 J
- D 50 J
What is the kinetic energy of a 2 kg body moving at 3 m/s?
- A 18 J
- B 6 J
- C 3 J
- D 9 J
A machine does 600 J of work in 10 s. What is its power?
- A 60 W
- B 6000 W
- C 6 W
- D 600 W
What is the gravitational potential energy of a 5 kg mass lifted 2 m? (g = 10 m/s²)
- A 50 J
- B 10 J
- C 100 J
- D 25 J
A ball dropped from a height of 5 m reaches the ground with what speed? (g = 10 m/s², no air resistance)
- A 100 m/s
- B 50 m/s
- C 10 m/s
- D 5 m/s
One kilowatt-hour is equal to:
- A 6 x 10⁴ J
- B 3.6 x 10⁶ J
- C 1 x 10³ J
- D 3.6 x 10³ J
Answer key
1. D, 2. D, 3. A, 4. C, 5. C, 6. B
W = F x d = 10 x 5 = 50 J.
KE = 1/2 mv² = 0.5 x 2 x 9 = 9 J.
Power = work / time = 600 / 10 = 60 W.
PE = mgh = 5 x 10 x 2 = 100 J.
Potential energy turns into kinetic energy: mgh = 1/2 mv², so v = sqrt(2gh) = sqrt(100) = 10 m/s.
1 kW x 1 h = 1000 W x 3600 s = 3.6 x 10⁶ J.