Question

A ball of mass 8kg falls from rest from a height of 100m neglecting air resistance. Calculate its kinetic energy after falling a distance of 30m(take g=10m/s^2).

Answer 1

Vf^2 = Vo^2 + 2g*d.
Vf^2 = 0 + 20*30 = 600.
Vf = 24.5 m/s. = Final velocity.

KE = 0.5m*V^2 = 4*(24.5)^2 = 2400 J.

Answer 2

PE at 100m=mgh
=2*10*100
=20*100
=2000J
PE at 30m=mgh
=2*10*30
=20*30
=600J
total energy at 30m=PE KE
2000=600 KE
2000-600=KE
KE=2000-600
KE=1400J
=14kj

Answer 3

PE max = Mg*hmax = 80*100 = 8000 J.

At ht. of 100 m, KE = 0; PE = 8000 J.
KE + PE = 0 + 8000 = 8000 J.

At ht. of 70 m. above gnd.
PE = Mg*h = 80*70 = 5600 J.
KE + PE = 8000
KE + 5600 = 8000
KE = 8000-5600 = 2400 J.

Answer 4

A ball of mass 8kg falls from rest from a height of 100m neglecting air resistance. Calculate it's kinetic energy after falling a distance of 30m (take g=10 miter per second square)