a ball of mass 8kg falls from rest from a height of 100m negleting a resistant calculate its kinetic energy after falling a distance of 30m (take gravity as 10m/s?

Answer 1

how long does it take to fall 30m?
30 = 5t^2
t = √6

what's its speed then?
v = 10t = 10√6

what's its KE then?
KE = 1/2 mv^2 = (1/2)(8)(600) = 2400 J

Or, using PE lost = KE gained:

starting PE = mgh = (10)(8)(100) = 8000
PE at 70m = (10)(8)(70) = 5600
PE lost = 2400 = KE gained.