1. A 15-kg rock falls from a cliff at a height of 140 m to a cliff that is 36 m above the ground. How fast is the rock falling when it strikes the lower cliff? (45 m/s)
2. A 2.00-kg block of ice is sliding across a frozen pond at 3.00 m/s. A 12-N force is applied in the direction of motion. After the ice block slides 17.0 m, the force is removed. The work done by the applied force is
3. A 5.0-kg ball on the end of a string is whirled at a constant speed of 1.0 m/s in a horizontal circle of radius 5 m. What is the work done by the centripetal force during one revolution?
4. A woman stands on the edge of a cliff and throws a stone vertically downward with an initial speed of 15 m/s. The instant before the stone hits the ground below, it has 2000 J of kinetic energy. If she were to throw the stone horizontally outward from the cliff with the same initial speed of 15 m/s, how much kinetic energy would it have just before it hits the ground?
5. Mike is cutting the grass using a human-powered lawn mower. He pushes the mower with a force of 100 N directed at an angle of 20° below the horizontal direction. Calculate the work that Mike does on the mower in pushing it 5 m across the yard.
6. The kinetic energy of a car is 7000 J as it travels along a horizontal road. How much work is required to stop the car in 20 s?
7. A 1500-kg car travels at a constant speed of 30 m/s around a circular track that is 100 m across. What is the kinetic energy of the car?
8. Use the work-energy theorem to find the force required to accelerate an electron (m =9.11 × 10−31 kg) from rest to a speed of 1.50 × 109 m/s in a distance of 1.25 m.
9. A 1000-kg elevator moves upward with constant speed through a vertical distance of 50m. How much work was done by the tension in the cable?
10. A 15-kg block is lifted vertically 10 meters from the surface of the earth. To one significant figure, what is the change in the gravitational potential energy of the block?
11. An engineer is asked to design a playground slide such that the speed a child reaches at the bottom does not exceed 4.0 m/s. Determine the maximum height that the slide can be.
12. A warehouse worker uses a forklift to lift a crate of pickles on a platform to a height 5 m above the floor. The combined mass of the platform and the crate is 100 kg. If the power expended by the forklift is 2000 W, how long does it take to lift the crate?
Answers: 1) (45 m/s) 2) 204 J, 3) 0 J, 4) 2000 J, 5) 470 J, 6) -7000 J, 7) 6.75x105 J, 8) 8.20x10-13 N, 9) 4.9x105 J, 10) 1000 J, 11) 0.816 m, 12) 2.45 s
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