Question

Just before striking the ground, a 2.0kg mass has 400J of kinetic energy. If friction can be ignored, from what height was it dropped?(g = 9.8m/s2)

Answer 1

Concept Law of Conservation of Energy

Conservation of energy means conservation of all forms of energy together. Accounting all forms of energy within an isolated system, the total energy remains constant. The mechanical energy accounts for only two forms of energy, namely kinetic energy, K and potential energy, U.

 

If only conservative forces act on a system, then total mechanical energy of the system remains constant. i.e. K+U = constantK+U=constant  

By conservation of mechanical energy,

 

Uf+Kf = Ui+Ki

 

or,0+Kf = mgh+0.  

H= k_f/mg=400/2×9.8= 20.4m

 

 

By conservation of mechanical energy, Uf+Kf = Ui+Ki