Unit 9 Work, Power, and Energy CW 01 2
Physics
CW 01: Work, Power, and Energy
Name: ______Date: ______Period: ______
You must show the work that leads to your answer to receive credit. The answer must include the appropriate unit.
______1. A car’s steering wheel has a diameter of 0.30 m if a force of
20 N is required to turn the wheel. How much work is done when the wheel is turned 2 revolutions? [W = F x d; answer: 37.7 J]
______2. A wagon requires 50 N to pull it. What power is needed to
pull it at a velocity of 5 m/sec? [P = F x v; answer: 250 watts]
______3. A 30 kg boy slides down a slide 4 m high. What is his velocity
at the bottom? [Ep = Ek; mgh = ½ mv2; answer = 8.85 m/sec]
______4. A 1500 kg car is going 20 m/sec. The car’s brakes exert a
force of 500N. What distance will the car go before it stops?
[kinetic energy of car = work done by brakes; ½ mv2 = F x d; answer = 600 m]
______5. A power drill exerts 40 Nm of torque as it drills a hole. It
spins at 300 rpm. What is the power? [P = Tω; answer = 1256 watts]
______6. A 4 kg bowling ball rolls at 3 m/sec. How much kinetic energy
does it have? [Eroll = ½ mv2 + ½ Iω2 or Eroll = 0.70 mv2:
answer = 25.2 J]
______7. A 3 kg rock is dropped from a height of 20 m onto a spring
which will absorb the impact. The spring has a K = 400 N/m. How far will the spring compress? [mgh = ½ Kx2; answer = 1.71 m]
______8. How long will it take a truck of mass 5000 kg with a power of
75 kilowatts to climb a 50 m hill? [P = (Fxd)/t; answer = 32.7 sec]
______9. The gunpowder in a cartridge has 5000 J of chemical energy. If all the energy is absorbed by the bullet, at what velocity does a 0.010 kg bullet leave the gun?
[Ek = ½ mv2; chemical energy = kinetic energy; answer = 1000 m/sec]
______10. It requires 4 N to stretch a spring 0.30 m. How much work is
done? [W = ½ F x d; answer = 0.60 J]