Work, Power, and Energy

A student pushes a 20.0 kg box with 50.0 N over 4.0 m. How much work is done?

• 2.0x10^2 J

• 2.5x10^2 J

• 1.0x10^2 J

• 20 J

Answer explanation

W = F × d = 50 N × 4 m = 200 J

You lift a 2.0 kg book 1.5 m high. What is the gain in potential energy (g=9.8)?

• 2.9 x10 J

• 19.6 x10^2J

• 9.8 x10 J

• 39.2 J

Answer explanation

PE = mgh = 2×9.8×1.5 = 29.4 J

A 0.50 kg toy car rolls down reaching 3.00 m/s. What is its KE?

• 2.25 J
• 4.5 J
• 0.75 J
• 1.5 J

Answer explanation

KE = 1/2 mv² = 0.5×0.5×9 = 2.25 J

A spring with F=200 N is stretched 0.005 m. How much work is done?

• 1 J
• 2 J
• 0.1 J
• 10 J

Answer explanation

W = Fd = 200×0.005 = 1 J

A 60.0 W bulb runs for 2.00 hours. How much energy is used?

• 4.32 x10^5 J

• 12.0 x10^3 J

• 7.20 x10^3 J

• 3.60 x10^3 J

Answer explanation

E = P×t = 60 W×7200 s = 432000 J

A 1.00 kg ball dropped from 2.00 m. What is its PE just before hitting?

• 19.6 J
• 9.8 J
• 29.4 J
• 0 J

Answer explanation

PE_initial = mgh = 1×9.8×2 = 19.6 J

You do 150.0 J of work pushing a sled up a 2.0 m incline (m=5.0 kg). What is the friction work?

• 52 J
• 98 J
• 150 J
• 0 J

Answer explanation

ΔPE=5×9.8×2=98 J; friction=150−98=52 J

A 0.2 kg car at 5.0 m/s stops in 2.0 m. What is the kinetic energy of the car?

• 1.25 J

• 2.5 J

• 0.5 J

• 2.5 N

Answer explanation

ΔKE=0.5×0.2×25=2.5 J

A 0.5 kg book is lifted 1.0 m. What is the potential energy?

• 4.9 J

• 4.9 m/s

• 3.8 J

• 3.8 m/s

Answer explanation

PE = mgh = .5x9.8x1 = 4.9 J

A pump lifts 10.0 kg of water 5.0 m in 10.0 s. What power is required?

• 49 W
• 490 W
• 5 W
• 98 W

Answer explanation

W=mgh=490 J; P=W/t=490/10=49 W