Question

A block of wood resting on an inclined plane of angle $ 30{}^\circ $ , just starts moving down. If the coefficients of friction is 0. 2, its velocity (in ms-1) after 5 s is: $ (g=10m{{s}^{-2}}) $

• A. 12. 75
• B. 16. 35
• C. 18. 25
• D. 20

Answer 1

The Correct Option is B

Acceleration of block down the plane. $ a=\frac{\mu \,mg\,\cos \theta -mg\,\sin \,\theta }{m} $ $ =\mu g\cos \theta -g\sin \theta $ $ =0.2\times 10\times \cos {{30}^{o}}-10\times \sin {{30}^{o}} $ $ =2\times \frac{\sqrt{3}}{2}-10\times \frac{1}{2} $ $ =\sqrt{3}-5 $ $ =1.73-5 $ $ =-3.278\,m/{{s}^{2}} $ From equation of motion, $ v=u-at $ Velocity after 5 s $ v=0+0.327\times 5 $ $ =16.35\,\,m/s $