A very heavy body moving at 20 m/s collides elastically head-on with a light stationary object. Find light object's speed (m/s) after impact in the limit M≫m.
Physics · Mixed Chapter
JEE Main Practice

Question

A very heavy body moving at 20 m/s collides elastically head-on with a light stationary object. Find light object's speed (m/s) after impact in the limit M≫m.

G1 Physics · Accepted Answer

Step 1: For one-dimensional elastic collision, speed of the initially resting light mass is v₂=2M/(M+m)·u₁. Step 2: In the heavy-mass limit M≫m, 2M/(M+m)→2. Step 3: Hence v₂≈2×20=40 m/s. This uses the 'heavy' limit specified in the source.