Question

An engine increases its angular speed 300 rpm to 900 rpm in 5 seconds. Number
of revolutions made during this time by the engine is
1) 100
2) 75
3) 50
4) 25
​

Answer 1

Answer:

The correct answer will be option 3 , 50

Explanation:

According to the problem the initial angular speed is ,

omega(i) = 2πN/60 = 10π [ where N = 300 rpm]

the final angular speed is,

omega(f) = 2πN/60 = 30π [where N = 900 rpm]

Therefore the acceleration of the engine is a(eng) = omega(f) -omega(i)/t

                        a(eng) = 30π-10π/5 = 4π rad/s^2

Now the number of revolutions= omega(i) x t +1/2a(eng) x t^2

                                                     = 10π x 5 x 1/2 x 4π x 25

                                                    = 50