Question

A ball thrown up vertically return to the earth after 12s. Find the velocity with which it
was thrown up? (g= 9.8m/s?)
(a) 29.4m's
(b) 58.8 m/s
(c) 36.5m/s
(d) 48.8m/s​

Answer 1

Answer.   29.4 pleas follow

Answer 2

Given:

✰ The time taken by the ball to reach maximum height ( t ) = 6s

✰ Acceleration due to gravity ( g ) = 9.8 m/s

✰ Final velocity ( v ) = 0 m/s

To find:

✠ The velocity with which it was thrown up.

Solution:

Explanation why we use 6s instead of 12s in equation:

[ The ball returns to the ground after 12s.

The ball takes total time 12s to go upward and come downward.

➣ Thus, the time taken by the ball just to go upward = 12/2 = 6s ]

When a body which is given with final velocity ( v ), such that the change in velocity takes in time ( t ) and we have acceleration due to gravity ( g ) then we will use first equation of motion to find initial velocity (u) .

Using first equation of motion,

➤ v = u + at

If body is rising vertically upward then, a = - g

➤ v = u - gt

put the values in,

• 0 = u - 9.8 × 6

• 0 = u - 58.8

• u = 0 + 58.8

• u = 58.8 m/s

∴ The velocity with which it was thrown up = 58.8 m/s

Option (b) 58.8 m/s is correct ✓

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