According to Newton's Second Law, what happens to the force if mass doubles while acceleration stays the same?

• A. It quadruples
• B. It stays the same
• C. It doubles
• D. It halves

Answer: (C)

When acceleration is kept constant, force is directly proportional to mass because F = m a. If mass doubles while a stays the same, the product m a doubles, so the force must double. Think of pushing a cart: with the same speed of acceleration, a heavier cart requires a stronger push, exactly doubling the force if the mass doubles. A quadruple force would require something else to change (like acceleration or mass changing by more than a simple doubling); the force staying the same would mean mass or acceleration didn’t change; halving the force would require mass to halve or acceleration to drop. So the force doubles.