Question 32: Centre of Mass and Rotational Motion

Question

Applying a constant torque the speed of a flywheel is increased from 1800 rpm to 2400 rpm in 10 seconds. The number of revolutions made by the flywheel during this time is:

Accepted Answer

LetÃ¢ÂÂs work in revolutions per second (rps) and use the fact that with constant torque (hence constant angular acceleration) the average speed times time gives total revolutions.
Convert speeds:
$$n_i = \frac{1800m\,rpm}{60} = 30m\,rps,\quad      n_f = \frac{2400m\,rpm}{60} = 40m\,rps.$$
Average speed:
$$\bar n = \frac{n_i + n_f}{2} = \frac{30 + 40}{2} = 35m\,rps.$$
Total revolutions in $t=10$Ã¢ÂÂs:
$$N = \bar n 	imes t = 35 	imes 10 = 350.$$
Answer: 350 (Option A).

Answer

350

Answer

900

Answer

700

Answer

2100

Centre of Mass and Rotational Motion

Applying a constant torque the speed of a flywheel is increased from 1800 rpm to 2400 rpm in 10 seconds. The number of revolutions made by the flywheel during this time is:

Choose the correct answer: