A body of mass falls freely from rest through a height of . What is its speed on reaching the ground? (take , answer in m/s)

Answer and explanation

Correct answer: D. 40

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  1. Step 1: By conservation of mechanical energy or the third equation of motion (), the speed of an object falling from rest through height is (independent of mass ).
  2. Step 2: Substitute and : .
  3. Step 3: Take the square root: .
Answer
40.
Why not the others: '20' adds rather than subtracts the constant term in the final step in evaluating ; '80' simply quotes the drop height as the velocity; '1600' calculates the gravitational potential energy in joules rather than velocity in m/s.

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