What is the kinetic energy of an object with a mass of #2 kg# that has been in freefall for #7 s#?

1 Answer
Mar 11, 2018

Answer:

#4705.96J#

Explanation:

Here we can solve the problem in three ways.

  1. Calculate the velocity after #7s#,it will be #v=9.8×7=68.6 ms^-1#

So,kinetic energy will be #1/2mv^2=1/2×2×68.6^2=4705.96 J#

2 . Find how much the object has come down in #7s# ,so it will be #s=1/2×9.8×7^2=240.1 m#(using #s=1/2 g t^2#)

So,gain in kinetic energy = loss of potential energy=#mgs=2×9.8×240.1=4705.96 J#

3 . Here work done by gravitational force in bringing the object by distance #s# in #7s# is stored in it as kinetic energy i.e #F×s=mg×s=2×9.8×240.1=4705.96J#