1. Which has the larger linear momentum: a 2,400kg houseboat going 6 m/s or a 670kg speedboat going 25 m/s?
2. A 8,500kg truck runs into the rear of a 1,000kg car that was stationary. The truck and car are locked together after the collision and move with speed 2 m/s. What was the speed of the truck before the collision?
3. In compressing the spring in a toy dart gun, 0.7 J of work is done. When the gun is fired, the spring gives its potential energy to a dart with a mass of 0.08 kg.
(a) What is the dart's kinetic energy as it leaves the gun?
(b) What is the dart's speed?
4. At NASA's Zero Gravity Research Facility in Cleveland, Ohio, experimental payloads fall freely from rest in an evacuated vertical shaft through a distance of 132 m.
(a) If a particular payload has a mass of 35 kg, what is its potential energy relative to the bottom of the shaft?
(b) How fast will the payload be traveling when it reaches the bottom of the shaft?
Convert your answer to mph for a comparison to highway speeds.
5. A bicycle and rider going 12 m/s approach a hill. Their total mass is 58 kg.
(a) What is their kinetic energy?
(b) If the rider coasts up the hill without pedaling, how high above its starting level will the bicycle be when it finally rolls to a stop?
6. A 1,000W motor powers a hoist used to lift cars at a service station.
(a) How much time would it take to raise a 1,450kg car 3 m?
(b) If the original motor is replaced with one rated at 2,000 W, how long would it take to complete this task?
7. A running back with a mass of 70 kg and a velocity of 6 m/s (toward the right) collides with, and is held by, a 105kg defensive tackle going in the opposite direction (toward the left). What is the velocity of the tackle before the collision for their velocity afterward to be zero? (Remember, velocity is a vector)
8. An elevator is able to raise 9,800 N to a height of 39 m in 11 s.
(a) How much work does the elevator do?
(b) What is the elevator's power output?
Show My Work (Optional)
9. It takes 130 minutes for a middleaged physics professor to ride his bicycle up the road to Alpe d'Huez in France. The vertical height of the climb is 1,120 m, and the combined mass of the rider and bicycle is 69 kg. What is the bicyclist's average power output?
10. When you throw a ball, the work you do to accelerate it equals the kinetic energy the ball gains. If you do twice as much work when throwing the ball, does it go twice as fast? Explain.
Yes. Twice as much work will give the ball twice as much kinetic energy. Since KE is proportional to the speed, the speed will double as well.
Yes. Twice as much work will give the ball four times as much kinetic energy. Since KE is proportional to the speed squared, the speed will be the square root of 4, or twice as fast.
No. Twice as much work will give the ball four times as much kinetic energy. Since KE is proportional to the speed, the speed will be four times larger.
No. Twice as much work will give the ball twice as much kinetic energy. But since KE is proportional to the speed squared, the speed will b2e times larger.
11. Describe the motion of an object that possesses kinetic energy yet undergoes no net displacement.
The object must be at rest.
The object must be sliding.
The object must be rolling.
The object must be falling. The object must be spinning.
12. If we know that a force of 5 N acts on an object while it moves 2 meters, can we calculate how much work was done with no other information? Explain your answer.
13. If you hold a ball at eye level and drop it, it will bounce back, but not to its original height. Identify the energy conversions that take place during the process, and explain why the ball does not reach its original release level.
When the ball strikes the floor, its ___ as it is flattened; this energy conversion is reversed during the rebound. On its way up after the ball bounces from the floor, its ____ until it reaches its highest point and stops. This point is below the original starting point because the ball has less energy-some of its original energy has been converted into ____.
14. An astronaut working with many tools some distance away from a spacecraft is stranded when the "maneuvering unit" malfunctions. How can the astronaut return to the spacecraft by sacrificing some of the tools?