Force of 20 N on 4 kg mass → acceleration.

**The reasoning** This is pure **Newton's Second Law**: F = ma (Force = mass × acceleration). You have: - Force (F) = 20 N - Mass (m) = 4 kg - Acceleration (a) = ? Rearrange the formula: a = F/m Substitute: a = 20/4 = **5 m/s²** That's it! When force pushes mass, acceleration is simply force divided by mass. --- **Why the wrong options tempt you** **A) 0.2 m/s²** — You divided mass by force (4/20) instead of force by mass. Classic reversal mistake! **C) 16 m/s²** — You subtracted: 20 − 4 = 16. Newton's law isn't subtraction; it's division. **D) 80 m/s²** — You multiplied: 20 × 4 = 80. This gives you force if you had acceleration, not the other way round. --- **Quick takeaway** **"To find acceleration, always divide the force by the mass—never multiply or subtract."** Remember: heavier objects (bigger mass) accelerate *less* for the same force, so division makes sense!