Question

A ball is in a hot air balloon that starts from rest at t = 0 and accelerates upwards at 2m/s². After 10s, the ball is dropped from the balloon.Draw ball's v - t graph:

• A.
• B.
• C.
• D.

Answer 1

The correct option is C

From v - t graph velocity should increase linearly till t = 10s and then decrease linearly after t = 10s.

V at t = 20s

$\Rightarrow$ v = u + at

$\Rightarrow$ v = 0 + 2(10)

= 20 m/s

Ball then has an acceleration of -10 m/s²

$\therefore$Time when v = 0, will be

v = u + at

0 = 10 + (-10)t

$\Rightarrow$ 0 = 20 - 10t

$\Rightarrow$ 20 = 10t

$\Rightarrow$ t = 2s

$\therefore$At t = 12s, velocity will be ______

Velocity will be negative after t = 12 s

$\therefore$Correct option is c.