(a) The roof of a large arena, with a weight of 350 kN, is lifted by 14 cm so th
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Question
(a) The roof of a large arena, with a weight of 350 kN, is lifted by 14 cm so that it can be centered. How much work is done on the roof by the forces making the lift? (b) In 1960 a Tampa, Florida, mother reportedly raised one end of a car that had fallen onto her son when a jack failed. If her panic lift effectively raised 4000 N (about 1/4 of the car's weight) by 5 cm, how much work did her force do on the car?
A cave rescue team lifts an injured spelunker directly upward and out of a sinkhole by means of a motor-driven cable. The lift is performed in three stages, each requiring a vertical distance of 9.10 m: (a) the initially stationary spelunker is accelerated to a speed of 3.60 m/s; (b) he is then lifted at the constant speed of 3.60 m/s; (c) finally he is decelerated to zero speed. How much work is done on the 67.0 kg rescue by the force lifting him during each stage?
During spring semester at MIT, residents of the parallel buildings of the East Campus dorms battle one another with large catapults that are made with surgical hose mounted on a window frame. A balloon filled with dyed water is placed in a pouch attached to the hose, which is then stretched through the width of the room. Assume that the stretching of the hose obeys Hooke's law with a spring constant of 62.0 N/m. If the hose is stretched by 2.80 m and then released, how much work does the force from the hose do on the balloon in the pouch by the time the hose reaches its relaxed length?
Explanation / Answer
(a)
Work done on the roof by the forces making the lift,
W = F.d
W = 350*10^3 * 0.14
W = 49000 J
W = 49 kJ
(b)
Work done by force on the car,
W = F.d = 4000 * 0.05
W = 200 J
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