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Standard XII

Physics

Work Energy Theorem

A force of 20...

Question

A force of $20 N$ is applied on a body of mass $5 k g$ resting on a horizontal plane. The body gains kinetic energy of $10 J$ after it moves a distance of $2 m$ . The frictional force is

$10 N$

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$15 N$

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$20 N$

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$30 N$

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Solution

The correct option is B
$15 N$

Step 1: Given data
Force, $F = 20 N$
Mass of body, $m = 5 k g$
Kinetic energy, $K . E = 10 J$
Distance, $s = 2 m$
Step 2: Find velocity
$\begin{array}{rcl} K . E & = & (1 / 2) m v^{2} \\ v^{2} & = & 2 K . E / m \\ v^{2} & = & \frac{2 \times 10}{5} \\ v^{2} & = & 4 \end{array}$
Step 3: Find acceleration
By Equation of motion
$v^{2} = u^{2} + 2 a s 4 = 0 + 2 x a x 2 a = 1 m / s$
Step 4: Find frictional force
$F_{s} = F - m a F_{s} = 20 - (5 \times 1) F_{s} = 15 N$
Hence, option B is correct.

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A force of 20N is applied on a body of mass 5kg resting on a horizontal plane. The body gains kinetic energy of 10J after it moves a distance of 2m. The frictional force is

A force of $20 N$ is applied on a body of mass $5 k g$ resting on a horizontal plane. The body gains kinetic energy of $10 J$ after it moves a distance of $2 m$ . The frictional force is