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Work and Energy — Physics STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 SciencePhysicsWork and Energy5 Marks
Question
A 250g block slides on a rough horizontal table. Find the work done by the frictional force in bringing the block to rest if it is initially moving at a speed of 40cm/s. If the friction coefficient between the table and the block is 0.1, how far does the block move before coming to rest?
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Answer

Given, m = 250g = 0.250kg, u = 40cm/sec = 0.4m/sec$\mu=0.1,\ \text{v}=0$
Here, $\mu\text{R}=\text{ma}$ {where, a = deceleration}$\text{a}=\frac{\mu\text{R}}{\text{m}}=\frac{\mu\text{mg}}{\text{m}}=\mu\text{g}$
$=0.1\times9.8=0.98\text{m}/\text{sec}^2$
$\text{S}=\frac{\text{v}^2-\text{u}^2}{2\text{a}}$
$=0.082\text{m}=8.2\text{cm}$
Again, work done against friction is given by,$\text{w}=\mu\text{RS}\cos\theta$
$=0.1\times2.5\times0.082\times1(\theta=0^\circ)=0.02\text{J}$
$\Rightarrow\text{W}=-0.02\text{J}$

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