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:

  1. 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

$$ 150=1 \times 10 \times 20-\frac{1}{2} \times 1 \times v^{2} \Rightarrow v=10 m / s $$



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