Question

An object of mass 1kg is falling from the height h=10m.calculate
a) the total energy of an object at h=10m

b) potential energy of the object when it is at h=4m

c) kinetic energy of the object when it is at h=4m

d) what will be the speed of the object when it hits the ground

Answer 1

Given:

$m=1\:{\rm kg},\quad h=10\: {\rm m},\quad g=9.8\: \rm m/s^2$

a)

$$E=E_k+E_p=\frac{mv^2}{2}+mgh$$ $$=0+1*9.8*10=98\:\rm J$$

b)

$$E_p=mgh=1*9.8*4=39\:\rm J$$

c)

$$E_k=E-E_p=98-39=59\:\rm J$$

d)

$$E_{kf}=98\:{\rm J}=\frac{mv_f^2}{2}$$

$$v_f=\sqrt{2*98/1}=14\:\rm m/s$$