A box is 3.2 m from the open rear of a truck. Friction coefficient μ=0.2. Truck starts from rest at acceleration 2.1 m/s². With g=10 m/s², find time (s) when the box falls off.
Physics · Mixed Chapter
JEE Main Practice

Question

A box is 3.2 m from the open rear of a truck. Friction coefficient μ=0.2. Truck starts from rest at acceleration 2.1 m/s². With g=10 m/s², find time (s) when the box falls off.

G1 Physics · Accepted Answer

Step 1: Maximum frictional acceleration of box a_box=μg=0.2×10=2.0 m/s². Step 2: Truck acceleration is 2.1 m/s², so it outruns box with relative acceleration a_rel=2.1−2.0=0.1 m/s². Step 3: Relative displacement reaches 3.2 m when 3.2=½(0.1)t². Step 4: t²=64 ⇒t=8 s.