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Question:

The magnitude of the normal reaction that acts on the block at the point Q is:

22.5 N

7.5 N

8.6 N

11.5 N

Solution:

Using work energy theorem we get mgRsin30° + W = 1/2mv²
or 200 × 50 = v²/2
Thus we get v = 10 m/s
Now, the force equation gives:
N − mgcos60° = mv²/R
or, N = 5 + 5² = 7.5 N.