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

Answer: (B)

16. 35

Answer 2

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 $v=0+0.327\times 5$ $=16.35\,\,m/s$