Question

The motor of an engine is rotating about its axis with an angular velocity of 100 rev/m. If conies to rest in 15s, after being switched off. Assuming constant angular deceleration. What are the numbers of revolutions made by it before coming to rest?

• A. 12.5
• B. 40
• C. 32.6
• D. 15.6

Answer 1

Answer: (A)

12.5

Answer 2

$0={{\omega }_{0}}-\alpha t$ $\alpha =\frac{{{\omega }_{0}}}{t}=\frac{(100\times 2\pi )/60}{15}$ $=0.7\,\text{rad/s}$ Now, angle rotated before coming to rest $\theta =\frac{\omega _{0}^{2}}{2\alpha }$ $\theta =\frac{{{\left( \frac{100\times 2\pi }{60} \right)}^{2}}}{2\times 0.7}$ $=78.33\,\text{rad}$ Numbers of rotations $\eta =\frac{\theta }{2\pi }=12.5$