 A 20 kg chair has 250 J of potential energy relative to the ground. If the chair is dropped from its position, what is its speed when it strikes the ground?
- A 60 kg diver drops from a ledge that is 50 ft above the water. What is the speed of the diver upon hitting the water? Give your answer in meters per second and miles per hour.
- A large bird with a mass of 1.0 kg is flying at a height of 10.0 m at a speed of 10 m/s. What is the mechanical energy of the bird?
 A 60 kg diver jumps off a diving board upward with an initial velocity of 5 m/s. The diving board is 10 m higher than the water. What is the diver’s speed when just entering the water after the dive?
 A 6 kg box is traveling at a speed of 10 m/s. Suddenly, it comes across a rough patch in the ground, which exerts a friction force of 40 N on the box. How far will the box go before it stops?
- A boy walks up a 10 meter tall snow-covered hill and sleds down. When he reaches the bottom, the boy is moving at 7 m/s. What is the efficiency of the boy's sled ride?
- John weighs 80 kg, and eats a 1,000 J candy bar. If his body perfectly transforms the energy in the chocolate into kinetic energy, what is the fastest he can run?
- How much distance does it take to stop a car going 30 m/s (67 mph) if the brakes can apply a force equal to one half the car’s weight?
- Consider a rubber ball whose bounce has an efficiency of 80%. That means 80% of the kinetic energy before the bounce remains kinetic energy after the bounce. (The rest of the energy is converted to thermal energy.)
- If the ball drops from a height of 5 m, how high does it bounce back on the first bounce?
- How high does the ball bounce on the second, third, and fourth bounces?
- You can only apply a 200 N force but you need to make a 20 kg wagon of mulch travel at a speed of 10 m/s. How far do you have to push the wagon before its speed reaches 10 m/s if it starts from rest? You may assume no friction.
| | - A pitcher for a baseball team can throw a fastball that travels at 45 m/s (100.6 mph). The pitcher throws a ball directly upward with the same energy that he uses to throw a fastball over the plate. Assume that the ball does not experience friction.
- How high does the baseball go?
- What is the speed of the baseball when the pitcher catches it?
- A 10 kg bowling ball sits at the top of a 10 m hill and then slides down its icy hillside.
- What is the speed of the bowling ball when it reaches the bottom of the hill?
- What is the change in kinetic energy of the system as the bowling ball travels from the top of the hill to the bottom of the hill?
- What is the bowling ball’s mechanical energy at the top of the hill?
- What is the bowling ball’s mechanical energy at the bottom of the hill?
- Juan, who is 60 kg, falls from a height of 20 m on a strange planet that has a large amount of air resistance and a gravity exactly equal to Earth’s. When he reaches the ground, he is traveling 2 m/s.
- How efficient was his jump at converting potential into kinetic energy?
- How much energy do Juan’s surroundings gain as he jumps?
- Nina, whose mass is 60 kg, is traveling on a bike at 15 m/s at the top of a 3.0 m hill. Nina continues down this hill without pedaling. Assume friction is negligible.
- What energy transformation is occurring as she travels down the hill?
- How fast is she traveling when she reaches the bottom of the hill?
- A 1,500 kg car begins at rest. A force of 2,000 N is applied to the car for a 20 m stretch in order to accelerate it. At the end of the 20 m, the car is going 5 m/s, and the road gains 21,250 J of thermal energy.
- Is energy conserved?
- Why does the road gain thermal energy?
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