Posted by **Josh** on Monday, December 10, 2012 at 7:00pm.

A brother (mass 20 kg) and his big sister (mass 32 kg) want to play on a teeter-totter. The beam is 7 m long and has a mass of 41 kg. Suppose the brother sits at the end of his side, 3.5 m away from the pivot point. How far away from the pivot point does the sister need to sit for the system to be in rotational equilibrium?

- physics -
**Mila**, Tuesday, April 16, 2013 at 11:37am
Use the center of mass fomula:

Xcm = (M1X1 + M2X2 + ... + MnXn)/(M1 + M2 + ... + Mn)

Don't forget the mass of the teeter-totter and its location at its geometric center (M1 = 41 kg, X1 = 3.5 since the fulcrum is in the middle of the beam).

Set the location of the sister at the origin (X = 0) and the brother at the opposite end of the beam (X = 7m).

Xcm = (20 x 7 + 32 x 0 + 41 x 3.5)/(20 + 32 + 41) = 283.5/93 = 3.05

The sister is 3.05 m from the pivot point.

## Answer this Question

## Related Questions

- Physics please help!! - A school yard teeter totter with a total length of 5.46 ...
- Physics - A child sits on one side of a teeter totter of length 7.60 m, a ...
- Physics - A child sits on one side of a teeter totter of length 7.60 m, a ...
- physics - Juggles the clown stands on one end of a teeter-totter at rest on the ...
- college physics - Juggles the clown stands on one end of a teeter-totter at rest...
- Physical Science - I need help with this problem because it is confusing me. I ...
- Physics - Suppose we take a 1 m long uniform bar and support it at the 27 cm ...
- Physics - a 10 foot long teeter-totter pivots in the middle. a 50 lb boy sits on...
- Physics URGENT!!! - Gayle runs at a speed of 9.00 m/s and dives on a sled, ...
- physics - Kevin has a mass of 77.5 kg and is skating with in-line skates. He ...