2) A 9,700-kg truck runs into the rear of a 1,000-kg car that was stationary. The truck and car are locked together after the collision and move with speed 3 m/s. What was the speed of the truck before the collision?
3)In compressing the spring in a toy dart gun, 0.8 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 40 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 13 m/s approach a hill. Their total mass is 62 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 1,000-W motor powers a hoist used to lift cars at a service station.
(a) How much time would it take to raise a 1,700-kg 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 76 kg and a velocity of 6 m/s (toward the right) collides with, and is held by, a 114-kg 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 45 m in 12 s.
(a) How much work does the elevator do?
(b) What is the elevator's power output?
9) It takes 140 minutes for a middle-aged 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 73 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.
11) Describe the motion of an object that possesses kinetic energy yet undergoes no net displacement.
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) During a head-on collision between two automobiles, the occupants are decelerated rapidly. Use the idea of work to explain why an air bag that quickly inflates in front of an occupant reduces the likelihood of injury. (Select all that apply.)
14) 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 .