Q 11-03-005NEETNEET 2021Top questionMedium
A car starts from rest and accelerates at $5\ \text{m/s}^2$. At $t = 4$ s, a ball is dropped out of a window by a person sitting in the car. What is the velocity and acceleration of the ball at $t = 6$ s ? (Take $g = 10\ \text{m/s}^2$)
Answer: (A) $20\sqrt{2}$ m/s, $10\ \text{m/s}^2$
At $t = 4$ s the car's speed is $5 \times 4 = 20$ m/s, so the ball leaves the window with a horizontal velocity of $20$ m/s. Once released, the only force on it is gravity.
At $t = 6$ s (2 s after release):
Horizontal velocity: $20$ m/s. Vertical velocity: $g \times 2 = 20$ m/s.
$$v = \sqrt{20^2 + 20^2} = 20\sqrt{2}\ \text{m/s}$$
Acceleration $= g = 10\ \text{m/s}^2$ (downward).
Solution by Sreeraj P, M.Sc Physics