1. A rock of mass m is thrown horizontally off a building from The speed of the

Question

1. A rock of mass m is thrown horizontally off a building from The speed of the rock as it leaves the thrower's hand at the edge of the building is vo is a height h, as shown above. the kinetic energy of the rock just before it hits the ground? (A) mgh (B) ½mVo2 (C) ½ mv,2-mgh (D) ½ mv,2 + mgh (E) mgh-½mvo2 2. A constant force of 900 N pushes a 100 kg mass up the inclined plane shown below at a uniform speed of 4 m/s. The power developed by the 900 N force is most nearly (A) 400 W (B) 800 W (C) 900 W (D) 1000 W (E) 3600 w A student weighing 700 N climbs at constant speed to the top of an 8 m vertical rope in 10 s. The average power expended by the student to overcome gravity is most nearly 3. (A) 1.1 W (B) 87.5 W (C) 560 W (D) 875 W (E) 5,600 w

Explanation / Answer

1. using energy conservation,

kinetic energy just before hitting groung = initial (kinetic + potential energy) = (1/2)mvo2 + mgh

2. power = F.v = 900 x 4 = 3600 W

3. avg power = F.(d/t) = 700 x (8/10) = 560 W

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