A 10 kg block is on a rough horizontal surface with μₛ = 0.4 and μₖ = 0.3. A horizontal force F = 2t N acts on it. Which graph correctly represents acceleration a versus time t? Take g = 10 m s⁻².

Question

G1 Physics · Accepted Answer

Maximum static friction is 0.4×10×10 = 40 N, so the block starts moving at t = 20 s. Just after motion begins, kinetic friction is 30 N, giving a = (40-30)/10 = 1 m s⁻² at t=20 s. Thereafter a = (2t-30)/10 = 0.2t-3, a straight line of slope 0.2. This is Image 2.