An electric motor rotating a workshop grinding wheel at a rate of 89 rev/min is switched off with a constant deceleration of 0.841 rad/s 2 . How long does it take for the grinding wheel to stop? Answer in units of s.

11.07s

Explanation:

Angular acceleration constant

w = w* + αt

The initial angular speed is

w* = 89 rev/min ( 2πrad/1rev)×(1min/60secs)

w* = 89rev/min(2×3.14rad/1rev)(1min/60secs)

= 558.93/60

= 9.315rad/s

The time to reach final speed = wf

Where wf = 0

α = -0.841rad/s ( the negative sign here is as a result of it deceleration)

t = wf - w*/α

Where

t is the time taken the s seconds

wf is the final angular speed

w* is the initial angular speed

t = 0 - 9.315/-0.841

t = -9.315/-0.841

t = 11.07s

i guess it’s a and b