A 60-kg teenager is standing on a skateboard. What force does the skateboard exert on the
teenager?

Force = mass x acceleration.

In this case , the acceleration is the one due to gravity, g. (Which is 9.81 m/s)

So

Force = mass x acceleration/force due to gravity  (or F = mg)

          = 60 x 9.81

          = 588.6 Newtons

answer; (arch); good luck

answer would be letter choice (a),   a ball resting on a shelf. would be another example of potential energy   >   stored energy > not moving.

a ball spinning on a finger   >   kinetic energy > moving energy

a ball rolling on the ground   >   kinetic energy   > moving energy

a   ball flying through the air   > kinetic energy   >   moving energy

hope that                                         : )