Question

The speed of a motor increases from 1200 rpm to 1800 rpm in 20s. How many revolutions does it make in
this period of time?
1) 400
2) 200
3500
4) 800​

Answer 1

Answer

500

Step-by-step explanation

ANSWER

Given,

ω

0

=1200rpm=20rps

ω=1800rpm=30rps

t=20sec

From the rotational mechanics

ω=ω

0

+αt

α=

t

ω−ω

0

α=

20

30−20

=0.5rps

2

The number of rotation,

θ=ω

0

t+

2

1

αt

2

θ=20×20+

2

1

×0.5×20×20

θ=400+100=500rotation