First slide

Kinetic energy

Question

A body of mass 5 kg is moving with a momentum of 10 kg-m/s. A force of 0.2 N acts on it in the direction of motion of the body for l0 seconds. The increase in its kinetic energy is

Moderate

A

2.8 joules
B

3.2 joules
C

3.8 joules
D

4.4 joules

Solution

Change in momentum = Force x time
$P_{2} - P_{1} = F \times t = 0.2 \times 10 = 2$
$\Rightarrow P_{2} = 2 + P_{1} = 2 + 10 = 12 kg - m / s$
Increase in K.E.
$= \frac{1}{2 m} ({P_{2}}^{2} - {P^{2}}_{1}) = \frac{1}{2 \times 5} [{(12)}^{2} - {(10)}^{2}]$
$= \frac{44}{10} = 4.4 J$

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