All forces, in any type of process or action, \"conserve\" total energy, which i

Question

All forces, in any type of process or action, "conserve" total energy, which includes heat, sound, chemical energy, etc. That means that the total amount of energy in all its forms after the process takes place is exactly the same as the total amount was before the process took place. Free fall is an example of conservation of energy If a object is released from a height ("h") and falls freely. it begins with only gravitational potential energy (PE and no kinetic. As it falls, PE is converted to KE, and just before it hits the ground, (h = 0), all of the original PE has been converted to KE. So, the final KE is equal to the original PE. Note that this only applies to free fall no significant air resistance. When the object hits the ground, its KE is converted to other forms of energy-heat, sound and the energy of material deformation a) A 0.40 kg rock is nudged off a bridge into a river below. If the rock begins with zero velocity and has a speed of 20 m/s just before it hits the water, how much kinetic energy did it have just before it hit the water? Use the approximate value of g, 10 m/s/s. b) Ignore air resistance. How much potential Energy did it have before it fell? c) What is the height of the bridge? d) New suppose the rock wasn't just dropped, but was tossed straight upward with an initial speed of 5 m/s. How much Kinetic energy did it have Just before it hit the water?

Explanation / Answer

a) from conservation of energu

potential energy = kinetic energy

k = 1/2mv^2 = 1/2*0.4*20^2 = 80 J

b) k = u

u = 80 J

c) mgh = 80

h = 80/0.4*10 = 20 m

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