Question

An alpha particle enters a hollow tube of 4 m length with an initial speed of 1 km/s. It is accelerated in the tube and comes out of it with a speed of 9 km/s. The time for which it remains inside the tube is

• A. $8 \times 10^{- 3}$s
• B. $80 \times 10^{- 3}s$
• C. $800 \times 10^{- 3}s$
• D. $8 \times 10^{- 4}s$

Answer 1

Answer: (D)

$8 \times 10^{- 4}s$

Answer 2

$v^{2} = u^{2} + 2as \Rightarrow (9000)^{2} - (1000)^{2} = 2 \times a \times 4$

$\Rightarrow a = 10^{7}m/s^{2}$Now $t = \frac{v - u}{a}$

$\Rightarrow \mspace{6mu} t = \frac{9000 - 1000}{10^{7}} = 8 \times 10^{- 4}\mspace{6mu}\sec$