A stone is dropped from a height of 245 m (g = 10 m/s^2, no air resistance). With what speed does it hit the ground?

Answer and explanation

Correct answer: B. 70 m/s

  1. Step 1: Energy conservation gives m g h = (1/2) m v^2, so v = sqrt(2 g h).
  2. Step 2: v = sqrt(2 x 10 x 245) = sqrt(4900) = 70 m/s.
Answer
70 m/s.
Why not the others: '2450 m/s' multiplies g by the height; '4900 m/s' gives v^2 and forgets the square root; '35 m/s' forgets the factor 2 inside the square root.

Practise more Mechanics, Heat, Electricity, Waves and Optics.

Free questions with an explanation for every one, and full timed Državna Matura (Bosnia & Herzegovina) mock tests.

All Mechanics, Heat, Electricity, Waves and Optics questionsTake a mock test

More Mechanics, Heat, Electricity, Waves and Optics questions