A 5 kg block on a horizontal surface has kinetic friction with μk = 0.30. If a 20 N push is applied, what is the resulting acceleration? (Use g ≈ 9.8 m/s^2)

• A. About 0.56 m/s^2
• B. About 1.06 m/s^2
• C. About 2.1 m/s^2
• D. About 3.0 m/s^2

Answer: (B)

When a block is pushed on a horizontal surface, its acceleration is determined by the net force after friction acts opposite to the motion. The normal force on a horizontal surface equals its weight: N = mg = 5 × 9.8 ≈ 49 N. The kinetic friction force is f_k = μk N = 0.30 × 49 ≈ 14.7 N. The push provides 20 N forward, so the net forward force is 20 − 14.7 ≈ 5.3 N. Using a = F_net / m gives a ≈ 5.3 / 5 ≈ 1.06 m/s^2 in the push direction.