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An object of 40 kg in raised to a height of 5m above the ground. What is its potential energy? If the object is allowed to fall, find its Kinetic energy when it is half-way down. (g = 10 ms–2)
Mass of the object m = 40 kg
Height h = 5m
Acceleration due to gravity,
g = 10 ms–2
∴ Potential energy = mgh
= 40 kg × 5m × 10 ms–2
= 2000J
When the object is half-way down, then the mass of the object = 40 kg
height h = 2.5m
Acceleration due to gravity,
g = 10 ms–2
From the third equation of motion
v2 - u2 = 2as
v2 = u2 + 2as
v2 = 0 + 2 x 10 x 2.5
v2 = 50 ms–1
Kinetic energy K.E. = 1/2 mv2
K.E. = 1/2 x 40 x 50
K.E. = 1000 J
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