Question

The roof of a large arena, with a weight of 340 kN, is lifted by 21 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?

Answer 1

Sol::

Given:
a) weight= 340 kN,
is lifted by d = 21 cm = 0.21 m

b) 4000 N (about 1/4 of the car's weight)

d = 5 cm=0.05 m

We have

work = force * displacement
W=F*d

part a)

If you count the displacement as the distance the roof or car were raised (and not counting the lowering of the roof and car after raise) then work will be

work=0.21 * 340,000*cos0°
=71400 Nm Or J

part b)

If you don't count the distance that the car was lowered then the work will be

work=0.05 * 4000*cos0°
= 200 Nm or J

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