Question # 1 A 71 kg student runs up the stairs in the time 13 s . The height of

Question

Question # 1

A 71 kg student runs up the stairs in the time 13 s . The height of the stairs is 12 m . What is his power output?

Question # 2

A horizontal spring with spring constant 130 N/mis compressed 15 cm and used to launch a 2.8 kgbox across a frictionless, horizontal surface. After the box travels some distance, the surface becomes rough. The coefficient of kinetic friction of the box on the surface is 0.15.

Use work and energy to find how far the box slides across the rough surface before stopping.

Explanation / Answer

1) power = energy/time

power = mgh/t

p = 71*9.8*12/13 = 642.28 W

2) k = 130 N/m

x = 0.15 m

before the rough surface

1/2mv^2 = 1/2kx^2

v = 1.02 m/s

this is the initial velocity of the rough surface

w = k

mue*mgd = 1/2mv^2

d = v^2/2*mue*g = 0.36 m

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