How much energy does a 10 N doll have sitting on a 4 m high countertop?

Awave is produced in a rope. the wave has a speed of 33 m/s and a frequency of 22 hz.

A100 kg running back runs at 5m/s into a stationary linebacker. it takes 0.5 for the running back to be completely stopped

Under the action of a constant force an object accelerates at 7.8 m/s2. what will the acceleration be if (a) the force is halved? (b) the object's mass is halved? (c) the force and the object's mass are both halved? (d) the force is halved and the object's mass is doubled?