A frictionless slide is 20 m high. A child starts from rest at the top. Taking g = 10 m/s^2, what is the child's speed at the bottom?
Answer and explanation
Correct answer: B. 20 m/s
- Step 1: Energy conservation: m g h = (1/2) m v^2.
- Step 2: v = sqrt(2 g h) = sqrt(2 x 10 x 20) = 20 m/s.
Answer
20 m/s.
Why not the others: The speed comes from the square root of 2gh; forgetting the root or the factor 2 gives the other values.
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