Question Detail
Question
A 15 g stopper is swung in a conical circle with a radius 0.80 m. The tension in the string is 1.5 N. If the speed of the stopper is 8.9 m/s, find the time taken for stopper to make 30 revolutions.
Correct Answer
Option E is the correct answer.
Detailed Explanation
The period T = circumference/speed = (2πr)/v = (2π × 0.80)/8.9 = (5.0265)/8.9 = 0.565 s per revolution. For 30 revolutions, time = 30 × 0.565 = 16.95 s ≈ 16.90 s. The tension given (1.5 N) is consistent with circular motion: T = mv²/r = 0.015 × (8.9)²/0.8 = 0.015 × 79.21/0.8 = 0.015 × 99.01 = 1.485 N, confirming the speed.
Hint
Find the period (time for one revolution) using T = 2πr/v, then multiply by the number of revolutions.