At the local playground, a 21-kg child sits on the right end of a horizontal teeter-totter, 1.8 m from the pivot point. on the left side of the pivot an adult pushes straight down on the teeter-totter with a force of 151 n. in which direction does the teeter-totter rotate if the adult applies the force at a distance of 3.0 m from the pivot? (clockwise/ counterclockwise)

Counterclockwise

Explanation:

We need to calculate the clocwkise and the counterclockwise torque.

The clockwise torque is the one generated by the child sitting on the right. This torque is given by:

where

is the force exerted by the child (his weight)

d = 1.8 m is the distance from the pivot point

So, the clockwise torque is

The counterclockwise torque is the one generated by the adult pushing on the left, and it is given by

where

F = 151 N is the force applied

d = 3.0 m is the distance from the pivot

Substituting,

So, the net torque is

And since the counterclockwise momentum is greater than the clockwise one, the teeter-totter will rotate counterclockwise.