A force of 20 N acts on a body of mass 4 kg for 5 s when it is initially at rest. Calculate the velocity acquired by the body and change in momentum of the body. [3 MARKS]

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Solution

Solution: 1 Mark per step

$S t e p 1 :$
Given, force, $F = 20 N$ , mass, $m = 4 k g$ , initial velocity $u = 0$ and time, $t = 5 s$ .
Let acceleration be $a$ .
According to Newton's second law, $F = m a$ .
So, $a = \frac{F}{m} = \frac{20}{4} = 5 m s^{- 2}$

$S t e p 2 :$
Let the final velocity acquired by the body be $v$ .
$∵ v = u + a t$
$v = 0 + 5 \times 5 = 25 m s^{- 1}$

$S t e p 3 :$
Momentum $= m v = 25 \times 4 = 100 k g m s^{- 1}$

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