Solution:

Explanation:

• Torque (
  $\mathrm{<strong\; style=",\; Times,\; serif;display:\; inline\; !important"><span\; class="katex"><span\; class="katex-html"\; aria-hidden="true"><span\; class="base"><span\; class="mord\; mathnormal">\tau </span></span></span></span>)\; is\; given\; by</strong><span\; style=",\; Times,\; serif">:</span>}$ 

   

  $$\tau =\frac{dL}{d\mathrm{t<span\; style=",\; Times,\; serif"></span>}}$$where

  $\mathrm{L <span\; style=",\; Times,\; serif">is\; the\; angular\; momentum.</span>}$ 

• If
  $\tau = 0$ 

  , then: 

  $$\frac{dL}{dt} = 0 \Rightarrow L = \text{constant}$$L=constantThis means angular momentum is conserved.