An object has a mass of #2 kg#. The object's kinetic energy uniformly changes from #135 KJ# to # 36KJ# over #t in [0, 6 s]#. What is the average speed of the object?

1 Answer
Jun 11, 2016

Answer:

I found #9.2m/s#

Explanation:

We need the speed of the object at each instant so we can use the definition of Kinetic Energy #K=1/2mv^2# to find it:
#K_i=1/2mv_i^2#
and
#K_f=1/2mv_f^2#

using our data:
#135=1/2*2v_i^2#
#v_i=11.6m/s#

and

#36=1/2*2v_f^2#
#v_f=6m/s#

we can now use:
#v_f=v_i+at#
and find #a#:
#6=11.6+6a#
#a=-0.9m/s^2#
we now use:
#v_f^2=v_i^2+2as#
to find the distance:
#36=135-2*0.9*s#
#s=55m#
So:
#"average speed"="distance"/"time"=s/t=55/6=9.2m/s#