What is the kinetic energy of an object with a mass of #6# #kg# that has been in freefall for #8# #s#?

1 Answer
Jun 25, 2018

Answer:

There are a number of ways to do this, but I have outlined one below.

The kinetic energy is #E_k=18.4# #kJ#

Explanation:

We know how to find the velocity of an object that starts at rest and has been accelerating at a known rate for a known time. We also know how to calculate the kinetic energy of an object if we know its mass and velocity.

#v=u+at#, but #u=0#, so #v=at#.

The acceleration, of course, is just the acceleration due to gravity. I'll use the value #9.8# #ms^-2#.

#E_k=1/2mv^2# and we can substitute in our expression for the velocity (and the value for the mass).

#E_k=1/2(6)(9.8xx8)^2=18,440# #J=18.4# #kJ#

Not that technically, given we were given the data to only one significant figure, technically the answer is #20# #kJ#.