# 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.

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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 $210\ Joule$.

Updated on 10-Oct-2022 13:22:49