Question

If an object is thrown vertically up with the initial speed u from the ground, then the time taken by the object to return back to ground is
(a) u²/2g
(b) u²/g
(c) u/2g
(d) 2u/g

Answer 1

Answer :- (d)

Explanation :- case 1 :- when body moves upward direction.
intial velocity = u
final velocity = v = 0
now, v = u + at
Here, v = 0 , a = -g [ acceleration is downward direction]
0 = u - gt ⇒t = u/g
Maximum height = h
u² = 2gh ⇒h = u²/2g -----(1)

Case 2 :- when body moves downward direction.[ Falling from maximum height ]
initial velocity, u = 0
final velocity = v
use formula, s = ut + 1/2at²
here, s = -h , u = 0 and a = -g
-h = 0 - 1/2gt'²
-u²/2g = -gt'²/2 [ from equation (1)
t' = u/g

Hence, total time = t + t' = u/g + u/g = 2u/g
Hence, option (d) is correct

Answer 2

Answer:

option d

option d =2u/g is correct

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