Certain force acting on a 20kg mass changes it velocity from 5ms-'to 2ms- Calculate the work done by the force.
sayushsingh321:
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Mass, m = 20 kg
Initial velocity, u = 5 m/s
Final velocity, v = 2 m/s
Time, t = 1s
From first equation of motion
v = u + at
or, a = (v - u)/t
a = (2 ms-1 - 5 ms-1)/15
a = -3 ms-2
From third equation of motion,
v² - u² = 2as
⇒ (2ms-1)² - (5ms-1)² = 2 x (-3ms-²) x s
⇒ -21 m²s-² = -6 ms-² x s
⇒ s = 7/2 m
Work done = F x s
Force = m x a
Therefore,
W = m x a x s
= 20 kg x (-3ms-²) x 7/2 m
= -210 Joules
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