What is the kinetic energy of an object with a mass of #2 kg# that has been in freefall for #4 s#?

1 Answer
Dec 25, 2016

Answer:

The kinetic energy will be 1537 J.

Explanation:

After #4s# of freefall, the speed of a body will be

#v="g"t=9.8(4)=39.2m/s#

Its kinetic energy will be

#KE = 1/2mv^2=1/2(2)(39.2^2) = 1537 J#

You can also find this by conservation of energy methods

During the 4s it will fall a distance of

#y=1/2"g"t^2 = 1/2 (9.8)(4^2) = 78.4m#

The decrease in potential energy of the body will be
#DelatU=mgy=(2)(9.8)(78.4) = 1537 J#

This decrease in potential energy will equal its increase in kinetic energy.