A2-kg ball is held 4 m above the ground. relative to the ground its potential energy is

78.4 J

Explanation:

The gravitational potential energy of the ball (relative to the ground) is given by

where

m = 2 kg is the mass of the ball

g = 9.8 m/s^2 is the acceleration due to gravity

h = 4 m is the height of the ball above the ground

Substituting numbers into the formula, we find

acceleration = (change in speed) / (time for the change)

change in speed = (20-120)= -100 m/s.

1.5 min = 90 sec

acceleration = -100/90 = -1.11 m/s^2.

we don't care about the 150kg or the 2,500 meters. they don't make any difference.

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