Question

A 1.5 N stone is thrown vertically upward with an initial speed of 15 m/s. Calculate

a. P.E at the maximum height

b. K.E at the instant it will strike the ground

c. P.E after 1 s

d. K.E after 1 s

Answer 1

(a)

$$PE_{max}=mgh_{max}=\frac{mv_0^2}{2}\\ =\frac{1.5/9.8*15^2}{2}=17\:\rm J$$

(b)

$$KE_f=KE_i=\frac{mv_0^2}{2}\\ =\frac{1.5/9.8*15^2}{2}=17\:\rm J$$

(c)

$$PE=mgh=mg(v_0t-gt^2/2)\\ =1.5(15*1-9.8*1^2/2)=15\:\rm J$$

(d)

$$KE=KE_i-PE\\ =17\:\rm J-15\: J=2\: J$$