1. Two children of mass 20 kg and 30 kg sit balanced on a seesaw with the pivot point located at the center of the 6-meter seesaw. a) If the 20 kg child is located 2 meters left of the pivot point at what distance from the pivot point should the 30 kg child sit in order to maintain the balance? (b) A third child of 10 kg sits at the left end of the seesaw, where must the 30 kg child now sit to balance the seesaw?

2. Two children push on opposite sides of a door during play. Both push horizontally and perpendicular to the door. One child pushes with a force of 17.5 N at a distance of 0.600 m from the hinges, and the second child pushes at a distance of 0.450 m. a) What force must the second child exert to keep the door from moving? (b) What force must the second child apply if the force applied at a 30-degree angle with respect to the door. Assume friction is negligible.

3. A professional weight-lifter can bench 130 kg, lifting it 30 cm high. (a) How much work is the weight-lifter exerting? (b) If the weight-lifter does a set of 15 reps in 40 seconds, how much power is being used?