Question

Two particles, of masses $M$ and $2M$, moving, as shown, with speeds of $10\, m/s$ and $5\, m/s$, collide elastically at the origin. After the collision, they move along the indicated directions with speeds $\upsilon_1$ and $\upsilon_2$, respectively. The values of $\upsilon_1$ and $\upsilon_2$ are nearly :

• A. 3.2 m/s and 6.3 m/s
• B. 3.2 m/s and 12.6 m/s
• C. 6.5 m/s and 6.3 m/s
• D. 6.5 m/s and 3.2 m/s

Answer 1

Answer: (C)

6.5 m/s and 6.3 m/s

Answer 2

$M \times10 \cos30^{\circ} +2M \times 5\cos45^{\circ}$
$= 2M \times V_{1} \cos30^{\circ} + M V_{2} \cos 45^{\circ}$
$5\sqrt{3} + 5\sqrt{2} = 2v_{1} \frac{\sqrt{3}}{2} + \frac{v_{2}}{\sqrt{2}}$
$10 \times M \sin 30^{\circ} - 2M \times 5\sin 45^{\circ}$
$= M v_{2} \sin 45^{\circ} - 2M v_{1} \sin 30^{\circ}$
$5- 5\sqrt{2} = \frac{v_{2}}{\sqrt{2} } - v_{1}$
Solving $v_{1} = \frac{17.5 }{2.7 }\simeq 6.5 m/s$
$v_{2} \approx 6.3 \,m/s$