An elastic collision occurs between equal masses m1 = m2 = 1 kg. Initially m1 moves at 5 m/s and m2 is at rest. What is the final velocity of m1?

An elastic collision occurs between equal masses m1 = m2 = 1 kg. Initially m1 moves at 5 m/s and m2 is at rest. What is the final velocity of m1?

• A. 5 m/s
• B. 0 m/s
• C. -5 m/s
• D. 10 m/s

Answer: (B)

In a perfectly elastic collision, both momentum and kinetic energy are conserved. For two equal masses sliding along a line, they exchange velocities. Here one mass starts at 5 m/s and the other is at rest (0 m/s). After the collision, the moving mass takes on the other’s initial velocity, which is 0 m/s, so it stops. The second mass then carries the 5 m/s. The total kinetic energy remains the same (initial 12.5 J, final 0.5*1*0^2 + 0.5*1*25 = 12.5 J), confirming the exchange of velocities. Therefore, the final velocity of the first mass is 0 m/s.

In a perfectly elastic collision, both momentum and kinetic energy are conserved. For two equal masses sliding along a line, they exchange velocities. Here one mass starts at 5 m/s and the other is at rest (0 m/s). After the collision, the moving mass takes on the other’s initial velocity, which is 0 m/s, so it stops. The second mass then carries the 5 m/s. The total kinetic energy remains the same (initial 12.5 J, final 0.510^2 + 0.5125 = 12.5 J), confirming the exchange of velocities. Therefore, the final velocity of the first mass is 0 m/s.