Question

A particle is fired upward with a speed of 20 km/s. The speed with which it will move in interstellar space is

• A. 8.8 km/s
• B. 16.5 km/s
• C. 11.2 km/s
• D. 10 km/s

Answer 1

The correct option is B

16.5 km/s

From conservation of energy

$\frac{1}{2}m{v}^2=\frac{1}{2}m\left[\right(20{)}^2-v_e^2]$

Here, $v_e$ = escape velocity = $8\sqrt{2}$km/s

$\therefore$ $v^2=(20{)}^2-(8\sqrt{2}{)}^2$ or v = 16.5 km/s