To what height will an object rise if thrown vertically upward at 72 kmh⁻¹? [g = 9.8ms⁻²]

Correct answer: d 20.4 m

72 km/h = 72 × 1000/3600 = 20 m/s. At the highest point v = 0, so h = u²/2g = 400/(2 × 9.8) ≈ 20.4 m.

Why the other options are wrong

• a 264.49 km: 264.49 is 72² ÷ 19.6, which treats 72 as if it were in m s⁻¹, and the unit is not km either. First 72 km/h has to become 20 m/s.
• b 264.49 m: 264.49 m uses 72 directly as m/s without converting km/h. 72 km/h = 20 m/s, so h = 400/19.6 ≈ 20.4 m.
• c 20.4 km: The number is right but the unit is wrong: 20.4 km would be twenty kilometres, impossible for a thrown object. The working gives metres.