Horizontal projectile: how far does it land?
A ball is thrown horizontally at 10 m/s from the top of a 20 m cliff. Ignoring air resistance and using g = 10 m/s², how far from the base of the cliff does it land?
Answer B: explanation for every choice
A
This assumes a 1 s fall time. The fall actually takes 2 s.
B
Correct. Fall time: h = ½gt², so t = √(2 × 20/10) = 2 s. Horizontal distance = 10 m/s × 2 s = 20 m.
C
This uses a 4 s fall time, from 2h/g without taking the square root.
D
This multiplies the horizontal speed by the height, which has no physical meaning.
TakeawayHorizontal and vertical motion are independent. Fall time depends only on height.
Equation usedDisplacement with constant acceleration
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