(a) the roof of a large arena, with a weight of 430 kn, is lifted by 15 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) 64.5 kJ

(b) 800 J

Solution:

As per the question:

Weight, w = 430 kN =

Displacement, d = 15 cm = 0.15 m

Force, F = 4000 N

Displacement, d' = 5 cm = 0.05 m

Now,

(a) We know that work done in the given case equals the potential energy:

Work done, W = PE = mgd = wd =

W = 64.5 kJ

(b) We know that work done is the product of force and displacement and is given by:

W' = Fd' =

jupiter is the largest planet in our solar system, having a mass and radius that are respectively, 318 and 11.2 times that of earth. suppose that an object falls from rest near the surface of each planet and that the acceleration due to gravity remains constant during the fall. each object falls the same distance before striking the ground. determine the ratio of the time of fall on jupiter to that on earth.