A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope

Question

A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes an angle of 30 degree with the horizontal. The force he exerts is parallel to the slope. If the speed of the crate is constant, then the work done by the man is. -200 J 61 J 140 J 200 J 260 J An escalator is used to move 20 people (60 kg each) per minute from the first floor of a department store to the second floor, 5 m above. The power required is approximately 100 W 200 W 1000 W 2000 W 60, 000 W A kilowatt hour is a unit of: power energy/time work power/time force/distance A 2-kg block is thrown upward from a point 20 m above the Earth's surface. At what height above Earth's surface will the gravitational potential energy of the Earth-block system have increased by 500 J? 5 m 25 m 46 m 70 m 270 m

Explanation / Answer

5) height displaced d

so, sin30 = d/5

or, d= 2.5 m

now work done= 2.5 x 80 = 200 N-m = 200 J ans d)

6) FORCE = mg = 20 x 60 x 10 ( taking g= 10 m/s^2)

or, F = 12000 N

workdone = 12000 x 5 = 60000 Nm = 60000 J

POWER= w/t = 60000 J / 60 S = 1000 Watt (ans option c)

7)   The kilowatt-hour (symbolized kWh) is a unit of energy equivalent to one kilowatt(1 kW) of power sustained for one hour. One watt is equal to 1 J/s. One kilowatt-hour is 3.6 megajoules, which is the amount of energy converted if work is done at an average rate of one thousand watts for one hour.

8) gravitational potential energy = mgh

or, 500 J = 2 kg x 9.8 m/s^2 x h

or, h = 25.51m = 26 m approx

as it is already placed at 20 m height. so height of the block from earth surface is (20+26) = 46 m ans option c

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