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Certain force acting on a 20 kg mass changes its velocity from $5\ ms^{-1}$ to $2\ ms^{-1}$. Calculate the work done by the force.
Given:
mass $m=20\ kg.$
Initial velocity $u=5\ ms^{-1}$
Final velocity $v=2\ ms^{-1}$
To do: To calculate the work done by the force.
Solution:
As known, work done to change the velocity $=$ change in kinetic energy
$=K_2-K_1$
$=\frac{1}{2}mv^2-\frac{1}{2}mu^2$
$=\frac{1}{2}m( v^2-u^2)$
$=\frac{1}{2}\times20(2^2-5^2)$
$=10( 4-25)$
$=-21\times10$
$=-210\ Joule$
Thus, the work done to change the velocity is $210\ Joule$.
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