Question

A schoolyard teeter-totter with a total length of 6.3 m and a mass of 41 kg is pivoted at its center. A 16 kg child sits on one end of the teeter-totter.

Part A: Where should a parent push vertically downward with a force of 210 N in order to hold the teeter-totter level?

Part B: Where should the parent push with a force of 330 N ?

Part C: How would your answers to parts A and B change if the mass of the teeter-totter were doubled?

Answer 1

A) as child is sitting on the one end then Moment of child about center is given by,

Where m is massof child and L = 6.3m

g= 9.8m/s^2

so we get,

And for equilibrium to hold teeter totter torque on other side of Center of this must be same so,

So,

So parents has to hold  

l = 2.35m from center of toy

B) now if parent apply 330 N

Then

l = 1.496 m from Center he has to hold for keep steady

C). Now you see mass of teeter about center does not apply torque because distance from Center is zero so if you double that mass then in that it also not affect our result in part A or B