Question

An object performs upward journey under gravity in time t. The downward journey is

performed in time

a) t

b) t

2

c) 2t

d) t/2​

Answer 1

Answer:

t because upward journey and downward journey have same time

Answer 2

Answer:

a) t

Explanation:

According to the question,

let,

The initial velocity of the body for the upward motion = u

The final velocity of the body for the upward motion = v = 0

The initial velocity of the body for the downward motion = u = 0

The final velocity of the body for the downward motion = -v

The time taken for upward motion = t

The time taken for the downward motion = t*

gravity was taken for the upward motion = -g

gravity was taken for the downward motion = g

For the upward motion of the body

$v = u + at\\\\0 = u - gt\\\\t = \frac{u}{g}$

For the downward motion of the body

$v = u + at\\\\-v = 0 - gt*\\\\t* = \frac{v}{g}$

As we know that for the complete journey the displacement is zero

So using the third equation of motion.

$v^2 = u^2 + 2as\\\\v^2 = u^2 ~~~~~~~~...(s = 0)\\\\v = u$

Therefore

$t = \frac{u}{g} \\\\t* = \frac{v}{g} = \frac{u}{g} ~~~~~~~~~~~~ .....(v = u) \\\\then,\\\\t = t*$

Hence, the downward journey is performed in t time.