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. Required:
a. In which direction does the teeter-totter rotate if the adult applies the force at a distance of 3.0 m from the pivot?
b. In which direction does the teeter-totter rotate if the adult applies the force at a distance of 2.5 m from the pivot?
c. In which direction does the teeter-totter rotate if the adult applies the force at a distance of 2.0 m from the pivot?

As part of your daily workout, you lie on your back and push with your feet against a platform attached to two stiff springs arranged side by side so that they are parallel to each other. when you push the platform, you compress the springs. you do an amount of work of 79.0 j when you compress the springs a distance of 0.230 m from their uncompressed length. (a) what magnitude of force must you apply to hold the platform in this position? (b)how much additional work must you do to move the platform a distance 0.230 m farther? (c) what maximum force must you apply to move the platform a distance 0.230 m farther?