Question 1
The force applied to an object is doubled and, at the same time, its mass is halved. What happens to the acceleration?
The right answer is the one marked above.
The acceleration becomes four times as large. The two changes act together, so they multiply:
a = F ÷ m
(2F) ÷ (m ÷ 2) = 2 × 2 × (F ÷ m) = 4a
Doubling the force alone doubles the acceleration (a ∝ F). Halving the mass alone doubles it too (a ∝ 1 ÷ m). Both at once gives 2 × 2 = 4 times.