Question

an object falls from rest . what will be its kinetic energy during the fall at end of 3s( g=10m/s^2)

Answer 1

Time = 3s
Acceleration= 10 m/s^2
u=0
V= u+at =0+(-10*3)=-30 m/s
since you haven't mentioned anything about mass in your question .. i will assume the mass to be M ... and also.. i will assume that it hasnt reached the ground before 3s.
Kinetic Energy = 1/2 mv^2
= 1/2m (-30)^2
=450m Joules

Answer 2

you don't give the mass of object
So let the mass is m