(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

A merry-go-round in a playground has a radius of about 2 m and a mass of about 400 kg. Starting from rest, a parent begins to rotate it with constant angular acceleration. After 5 s, it reaches its final angular velocity of about pi/2 rad/s, and continues to rotate at that angular velocity

a.

Treat the merry-go-round as a uniform disk (the moment of inertia of a uniform disk is mr2/2); the final rotational kinetic energy of the merry-go-round is about ___ J.

b.

5 children, each with a mass of about 20 kg, step on the merry-go-round and stay near its edge. As they step on it, its angular velocity drops to about ____ rad/s. Ignore friction.

2. Relevant equations

I_disk=0.5mr^2

KE_rotational=0.5*I*w^2

3. The attempt at a solution

For part a I did...

KE=(0.5)(0.5)(400)(2^2)(pi/2)^2=987 J

For part b I did...

KE_i=KE_f

987 = 0.5(100)(2^2)(w^2) + 0.5(0.5)(400)(2^2)(w^2)

and get w=1.3 but the answer is supposed to be 1.0. Is mr^2 the correct way to do the kid's intertia?

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Merry-Go-Round physics homework

**Physics Forums | Science Articles, Homework Help, Discussion**