Question

A 100 kg disc with radius 1.6 m is spinning horizontally at 25 rad/s. You place a 20 kg brick quickly and gently on the disc so that it sticks to the edge of the disc. Determine the final angular speed of the disc-brick system.

Answer 1

20.83rad/s

Step-by-step explanation:

Using the law of conservation of momentum

m1u1+m2u2 = (m1+m2)v

m1 and m2 are the mass of the disc and Brick respectively

u1 and u2 are the linear velocities respectively

v is their final velocity of the block-disc system

Given

m1 = 100kg

m2 = 20kg

u1 = wr =25×1.6

u1 = 40m/s

u2 = 0m/s (brick is stationary)

Substitute and the final linear velocity v

100(40)+20(0) = (100+20)v

4000 = 120v

v = 4000/120

v = 33.3m/s

From the formula;

v = wr

w = v/r

w= 33.3/1.6

w = 20.83rad/s.

Hence the final angular speed of the disc-brick system is 20.83rad/s