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Homework answers / question archive / 1) In which one of the following situations is zero net work done? (a) A ball rolls down an inclined plane
1) In which one of the following situations is zero net work done? (a) A ball rolls down an inclined plane.
2. A concrete block is pulled 7.0 m across a frictionless surface by means of a rope. The tension in the rope is 40 N; and the net work done on the block is 247 J.
What angle does the rope make with the horizontal?
5. Which one of the following statements concerning kinetic energy is true?
6. The kinetic energy of a car is 8 ⋅ 10^{6} J as it travels along a horizontal road. How much work is required to stop the car in 10 s?
7. A 10.0-g bullet traveling horizontally at 755 m/s strikes a stationary target and stops after penetrating 14.5 cm into the target. What is the average force of the target on the bullet?
8.An elevator supported by a single cable descends a shaft at a constant speed. The only forces acting on the elevator are the tension in the cable and the gravitational force.
Which one of the following statements is true?
9. A 1500-kg elevator moves upward with constant speed through a vertical distance of 25
m. How much work was done by the tension in the cable?
(a) 990 J (c) 140 000 J (e) 430 000 J (b) 8100 J (d) 370 000 J
10. Two balls of equal size are dropped from the same height from the roof of a building. One ball has twice the mass of the other. When the balls reach the ground, how do the kinetic energies of the two balls compare?
11. A woman stands on the edge of a cliff and throws a stone vertically downward with an initial speed of 10 m/s. The instant before the stone hits the ground below, it has 450 J of kinetic energy. If she were to throw the stone horizontally outward from the cliff with the same initial speed of 10 m/s, how much kinetic energy would it have just before it hits the ground?
(a) 50 J (c) 450 J (e) 950 J (b) 100 J (d) 800 J
12. A block is dropped from a high tower and is falling freely under the influence of gravity. Which one of the following statements is true concerning this situation? Neglect air resistance.
Questions 13 and 14pertain to the situation described below:
A 2.0-kg projectile is fired with initial velocity components v_{ox} = 30 m/s and v_{oy} = 40 m/s from a point on the earth's surface. Neglect any effects due to air resistance.
16. A bicyclist is traveling at a speed of 20.0 m/s as he approaches the bottom of a hill. He decides to coast up the hill and stops upon reaching the top. Determine the vertical height of the hill.
(a) 28.5 m (c) 11.2 m (e) 20.4 m (b) 3.70 m (d) 40.8 m
17. An engineer is asked to design a playground slide such that the speed a child reaches at the bottom does not exceed 6.0 m/s. Determine the maximum height that the slide can be.
18. The initial velocity of a 4.0-kg box is 11 m/s, due west. After the box slides 4.0 m horizontally, its speed is 1.5 m/s. Determine the magnitude and the direction of the non conservative force acting on the box as it slides.
(a) 42 N, due west (c) 31 N, due east (e) 83 N, due west (b) 120 N, due east (d) 59 N, due east
19. An automobile approaches a barrier at a speed of 20 m/s along a level road. The driver locks the brakes at a distance of 50 m from the barrier. What minimum coefficient of kinetic friction is required to stop the automobile before it hits the barrier?
(a) 0.4 (c) 0.6 (e) 0.8 (b) 0.5 (d) 0.7
20. A 51-kg woman runs up a flight of stairs in 5.0 s. Her net upward displacement is 5.0 m.
Approximately, what average power did the woman exert while she was running?
(a) 5.0 kW (c) 0.75 kW (e) 0.25 kW (b) 1.0 kW (d) 0.50 kW
21. An escalator is 30.0 meters long and slants at 30.0° relative to the horizontal. If it moves at 1.00 m/s, at what rate does it do work in lifting a 50.0 kg man from the bottom to the top of the escalator?
(a) 49.3 W (c) 245 W (e) 495 W (b) 98.0 W (d) 292 W
22. A warehouse worker uses a forklift to lift a crate of pickles on a platform to a height 2.75 m above the floor. The combined mass of the platform and the crate is 207 kg. If the power expended by the forklift is 1440 W, how long does it take to lift the crate?
(a) 37.2 s (c) 3.87 s (e) 1.86 s (b) 5.81 s (d) 18.6 s
23. The amount on energy needed to power a 0.10-kW bulb for one minute would be just sufficient to lift a 1.0-kg object through a vertical distance of
24. The graph shows the force component along the displacement as a function of the magnitude of the displacement. Determine the work done by the force during the interval from 2 to 10 m.
25. A motorist driving a 1000-kg car wishes to increase her speed from 20 m/s to 30 m/s in 5 s. Determine the horsepower required to accomplish this increase. Neglect friction.
(a) 20 hp (c) 70 hp (e) 90 hp (b) 30 hp (d) 80 hp
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