How much energy is released when 2.8 kg of diethyl ether freezes?

A 2 kg rock is released from rest at a height of 29m. determine the kinetic energy?

• A 2 kg rock is released from rest at a height of 29m. Ignore air resistance and determine the kinetic energy, gravitational potential energy, and total mechanical energy at each of the following height. 20 m; 15m; 5m; 9 m.

• Answer:

  Gravitational potential energy is easy. E=mass*gravity*height = 2*9.8*20 = 392J (for a height of 20 meters). You can work out the rest by replacing the height with 15, 5 and 9. For Kinetic energy, E= 0.5*m*v². We have to work out v. v² = u² + 2as, where it says inital speed(u)=0, displacement(s)=29-20=9m (rock has fallen from 29m to 20m) and we already know acceleration = gravity = 9.8. So: v² = 0 + 2*9.8*9 v² = 176.4 v = sqrt(176.4) = 13.28 m/s. So kinetic energy = 0.5*2*(13.28)² = 176.4J after the rock has fallen 9 meters. Just do the same with different values for (s) depending on how far the rock has fallen from the initial position of 29 meters. :D For total mechanical energy at that height, I think you just add the gravitational and the kinetic energy that you worked out.