A block released from rest from the top of a smooth inclined plane of inclination 45∘ takes t seconds to reach the bottom. The same block released from rest from the top of a rough inclined plane of the same inclination of 45∘ takes 2t seconds to reach the bottom. The coefficient of friction is
0.75
The acceleration of the block sliding down the smooth inclined plane is a1=g sin θ and down the rough inclined plane is a2=g sin θ−μg cos θ .
Given t1=t and t2=2t
If the length of the inclined planes is s, we have
s=12a1t21=12a2t22⇒a1t21=a2t22⇒g sin θ×t2=(g sin θ−μg cos θ)×(2t)2⇒sin 45∘=4(sin 45∘−μ cos 45∘)⇒μ=34=0.75
Hence, the correct choice is (d).