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Standard XIII

Physics

Normal Force

A block of ma...

Question

A block of mass $m$ is placed on the floor of lift which is moving with velocity $v = 4 t^{2}$ , where $t$ is time in second and velocity in $m/s$ . Find the time at which normal force on the block is three times of its weight.

(\frac{3 g}{8}) s

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g s

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\frac{g}{4} s

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3 g s

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Solution

The correct option is C $\frac{g}{4} s$
Given velocity $v = 4 t^{2}$
$\Rightarrow$ acceleration $a = \frac{d v}{d t} = 8 t$
Now as lift is moving up
$N = m (g + a)$
$N = m (g + 8 t)$
Given $N = 3 m g$
$\Rightarrow 3 m g = m g + 3 m t$
$= 2 / m g = 8 / m t$
$\Rightarrow t = \frac{g}{4} s$

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A block of mass m is placed on the floor of lift which is moving with velocity v=4t2, where t is time in second and velocity in m/s. Find the time at which normal force on the block is three times of its weight.

The correct option is C g4sGiven velocity v=4t2 ⇒ acceleration a=dvdt=8t Now as lift is moving up N=m(g+a) N=m(g+8t) Given N=3 mg ⇒3mg=mg+3mt =2/mg=8/mt ⇒t=g4s

A block of mass $m$ is placed on the floor of lift which is moving with velocity $v = 4 t^{2}$ , where $t$ is time in second and velocity in $m/s$ . Find the time at which normal force on the block is three times of its weight.

The correct option is C $\frac{g}{4} s$
Given velocity $v = 4 t^{2}$
$\Rightarrow$ acceleration $a = \frac{d v}{d t} = 8 t$
Now as lift is moving up
$N = m (g + a)$
$N = m (g + 8 t)$
Given $N = 3 m g$
$\Rightarrow 3 m g = m g + 3 m t$
$= 2 / m g = 8 / m t$
$\Rightarrow t = \frac{g}{4} s$