Question

a lift is moving down with an acceleration equal to the acceleration due to gravity .a body of mass M kept on the floor of the lift is pulled horizontally. if the coefficient of friction is mu ,then frictional resistance offered by the body is

Answer 1

Answer: The frictional resistance offered by the body is zero.

Explanation:

Given that,

Acceleration of lift = acceleration due to gravity

Mass of the body = M

Coefficient of friction = $\mu$

Let us consider the mass of the lift is m.

Then,

The normal force is

$Mg-N = ma$

$N = Mg-ma$

We know that,

a = g

Therefor, the normal force is

$N = mg-mg$

$N = 0$

Now, the frictional force is

$F_{\mu} =\mu N$

Put the value of N

$F_{\mu} = 0$

Hence, the frictional resistance offered by the body is zero.

Answer 2

According to the given data, Newton’s law of motion will be applied and we get the equation for the motion as

$mg - N = ma$

$\Rightarrow N = m a - mg$

$\Rightarrow N = m ( a - g)$

but as given that a = g thereby

$N = m ( g -g)$

$\Rightarrow N = 0$

Therefore,

$F _{friction} = \mu N$

$\Rightarrow F _{friction} = \mu \times 0$

$\Rightarrow F _{friction} = 0$