1)

A wheel of moment of inertia 2 kg m2 is rotating about an axis passing through centre and perpendicular to its plane at a speed 60 rad/s. Due to friction, it comes to rest in 5 minutes. The  angular momentum of the wheel three minutes before  it slops rotating is 


A) 24 kg m2/s

B) 48 kg m2/s

C) 72 kg m2/s

D) 96 kg m2/s

Answer:

Option C

Explanation:

Given , l= 2 kg m2

 ω0 = 60 rad/s , ω =0

 t=5 min=5 x60= 300 s

 From the relation, 

ω=ω0+αt

α=ωω0t

    α=060300=60300=15rad/s2

 for t=2 min

 = 2 x 60=120 s

 ω=ω0+αt

= 6015×120=6024

     ω =36 rad/s

 As, angular momentum.  L= l ω

 substituting  the values  in the above relation, 

We get  L= 2 x36= 72 kg m2 /s