NEET 2019 Model Question Paper 2

The various forces acting on the body have been shown in the figure. The force on the body down the inclined plane in presence of friction µ is F=mg‌sin‌θ−f=mg‌sin‌θ−µN=ma
or a=g‌sin‌θ−µg‌cos‌θ
Since block is at rest thus initial velocity u = 0
Therefore, time taken to slide down the plane
t1=√

2s

a

=√

2s

g‌sin‌θ−µg‌cos‌θ

In absence of friction time taken will be
t2=√

2s

g‌sin‌θ

Given :t1=2t2
t12=4t22 or

2s

g(sin‌g‌q−µ‌cos‌θ)

=2s×4g(sin‌θ)
or sin‌θ=4‌sin‌θ−4µ‌cos‌θ orµ=

3

4

‌tan‌θ=0.75