A block A is placed over a long rough plank B of the same mass. The plank lies on a smooth horizontal surface. At t = 0 block A is given horizontal velocity v₀. Which graph correctly represents the velocities v₁ of A and v₂ of B versus time?

Question

G1 Physics · Accepted Answer

Friction slows A and accelerates B with equal-magnitude accelerations because the masses are equal. Total horizontal momentum is conserved, so both velocities become equal at v₀/2. Thus v₁ decreases linearly and v₂ increases linearly until they meet at v₀/2, as in Image 2.