Question

$\underline{ \underline{\huge \mathfrak{Question :-}}}$
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A ball is dropped from a height of 20 m. a second ball is thrown downwards from the same height after one second with initial velocity u. if both the balls reach the ground at the same time, calculate the initial velocity of the second ball.
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Answer with explanation please! ^^​

Answer 1

Given :-

A ball is dropped from a height of 20 m. a second ball is thrown downwards from the same height after one second with initial velocity u. if both the balls reach the ground at the same time,

To Find :-

Calculate the initial velocity of the second ball.

Solution :-

For ball no. 1

s = ut + 1/2at²

Here

s = h & a = g

⇒ h = ut + 1/2gt²

⇒ 20 = 0(t) + 1/2 × 10 × t²

⇒ 20 = 0 + 5t²

⇒ 20 = 5t²

⇒ 20/5 = t²

⇒ 4 = t²

⇒ √(4) = t

⇒ 2 = t

Time for ball 1 = 2 second

Time for ball 2 = 2 - 1 = 1 second

Now,

In case of ball 2

h = ut + 1/2gt²

⇒ 20 = u × 1 + 1/2 × 10 × (1)²

⇒ 20 = u + 5

⇒ 20 - 5 = u

⇒ 15 = u

Hence,

Initial velocity of ball is 15 m/s

[Note - You can use g as 9.8 m/s². There will be few changes only]