Question

A STONE THROWN VERTICALLY UPWARDS WITH INITIAL VELOCITY U REACHES A HEIGHT H BEFORE COMING DOWN .SHOW THAT THE TIME TAKEN TO GO UP IS SAME AS THE TIME TAKEN TO COME DOWN

Answer 1

Let us consider an object which is projected vertically upwards with initial velocity  u which reaches a maximum height h.

Acceleration due to gravity=-g

Equation of Motion for a body projected thrown upwards :
V=u-gt----------(1)

h=ut-1/2gt² -----------(2)

v²-u²=-2gh --------(3)

Equations of motion for freely falling body :
for free fall : 
Initial velocity=u=0
g=g
V=gt----------(4)
h=1/2gt²-------(5)
v²=2gh------(6)

Time of Ascent is the time taken by body thrown up to reach maximum height h At maximum height , V=0

Equation (1) turns to u=gt1t1=u/g  ----------(7)

Maximm height h=u²/2g ----------(8)

Time of descent : After reaching maximum height ,
 the body begins to travel downward like free fallso equation (5)

h=1/2gt₂²t₂²
=2h/gt₂=√2h/g

but from equation (9)

t₂=√2xu²/2g²
t₂=u/g -----------------equation (10)

∴t₁=t₂The time ascent is equal to time of descent in case of bodies moving under gravity.

Answer 2

It is because to acceleration due to gravity......