1.

A smooth inclined plane of length L, having an inclination theta with horizontal is inside a lift which is moving down with retardation a. The time taken by a block to slide down the inclined plane from rest will be

Answer»

`sqrt((2L)/(sqrt(a sin theta)))`
`sqrt((2L)/(g sin theta))`
`sqrt((2L)/((g-a) sin theta))`
`sqrt((2L)/((g+a) sin theta))`

SOLUTION :(d) Moving down with RETARDATION a MEANS, lift is accelerated upwards. With respect to lift, pseudo force on the block will be ma in downward direction, where m is the mass of block. So, downward force mg on the block will be replaced by m(g+a). Therefore, acceleration of block relative to PLANE will be,
`a_(R)=(g+a) sin theta`(down the plane)
From , `"" L=(1)/(2)a_(r)t^(2)"" (s=(1)/(2)at^(2))`
`t=sqrt((2L)/(a_(r)))=sqrt((2L)/((g+a)sin theta))`


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