A block of mass m is kept on a platform which starts from rest with constant acceleration g/2 upward, as shown in fig. Work done by normal reaction on block in time t is :

Question

A block of mass m is kept on a platform which starts from rest with constant acceleration g/2 upward, as shown in fig. Work done by normal reaction on block in time t is : (A) 0 (B) (3m g2 t2/4) (C)  - (m g2 t2/8) (D)  (m g2 t2/8)

Tardigrade Admin · Accepted Answer

Since the acceleration is in upward direction, there will be a pseudo force acting on the block given as:

< b r / > F_{p} = m \times \frac{g}{2} < b r / >

Now applying the force balance on the block

< b r / > N - m g = \frac{m g}{2} < b r / >

< b r / >\Rightarrow N = \frac{3 m g}{2} < b r / >

We know that the displacement of a body moving under gravity is given as

< b r / > S = u t + \frac{1}{2} g t^{2} < b r / >

Here initial velocity is zero.
Now, work done

W = N S = (\frac{3 m g}{2}) (\frac{1}{2} g t^{2})

< b r / >\Rightarrow W = \frac{3 m g ^{2} t ^{2}}{4} < b r / >

Q. A block of mass $m$ is kept on a platform which starts from rest with constant acceleration $g /2$ upward, as shown in fig. Work done by normal reaction on block in time $t$ is :

$0$

$\frac{3 m g ^{2} t ^{2}}{4}$

$- \frac{m g ^{2} t ^{2}}{8}$

$\frac{m g ^{2} t ^{2}}{8}$

Q. A block of mass m is kept on a platform which starts from rest with constant acceleration g/2 upward, as shown in fig. Work done by normal reaction on block in time t is :

0

43mg2t2​

−8mg2t2​

8mg2t2​

Q. A block of mass $m$ is kept on a platform which starts from rest with constant acceleration $g /2$ upward, as shown in fig. Work done by normal reaction on block in time $t$ is :

$0$

$\frac{3 m g ^{2} t ^{2}}{4}$

$- \frac{m g ^{2} t ^{2}}{8}$

$\frac{m g ^{2} t ^{2}}{8}$