JAMB Physics 2023 Paper

Concept:Forces are balanced because the box moves at constant speed, so the net horizontal and vertical forces are each zero.Explanation:Weight $W = 400$ N, applied force $P = 100$ N, and angle $\theta = 30^\circ$.Resolve the applied force: horizontal component is $P\cos30^\circ$, vertical component is $P\sin30^\circ$.The vertical component of $P$ presses the box downward, so the normal reaction is $R = W + P\sin30^\circ$.$R = 400 + 100\sin30^\circ = 400 + 50 = 450$ N.Since speed is constant, horizontal acceleration is zero: $P\cos30^\circ - F_r = 0$.Thus friction $F_r = 100\cos30^\circ$.Using $F_r = \mu R$, we get $\mu = \frac{100\cos30^\circ}{450}$.$\mu = \frac{86.60}{450} = 0.192 \approx 0.19$.Answer:A. 0.19