Class 11 NEET Physics Laws of Motion Questions

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−mu‌g‌cos‌θ
since block is at rest thus initial velocity u=0
∴ 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(sin‌θ−µ‌cos‌θ)

=

2s×4

g(sin‌θ)

or sin‌θ=4‌sin‌θ−4µ‌cos‌θ or µ=

3

4

‌tan‌θ=0.75