Work Power and Energy 3 Question 3
3. The speed of the block when it reaches the point $Q$ is
(a) $5 ms^{-1}$
(b) $10 ms^{-1}$
(c) $10 \sqrt{3} ms^{-1}$
(d) $20 ms^{-1}$
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Answer:
Correct Answer: 3. (b)
Solution:
- Height fallen up to point $Q$
$$ h=R \sin 30^{\circ}=40 \times \frac{1}{2}=20 m $$
Work done against friction =Initial mechanical energy
-Final mechanical energy
$$ =m g h-\frac{1}{2} m v^{2} $$
Putting the values, we get
$$ 150=1 \times 10 \times 20-\frac{1}{2} \times 1 \times v^{2} \Rightarrow v=10 m / s $$
