What is the velocity of the rock when it is 5.10m5.10m below the starting point (remember that velocity is a vector)?

Question

A person throws a rock straight downwards off a cliff with an initial speed of 13.0m/s13.0m/s. What is the velocity of the rock when it is 5.10m5.10m below the starting point (remember that velocity is a vector)? Treat the effect of air resistance to be negligible and the upwards direction as positive.

Answer 1

You are given the following information: v₀ = -13.0 m/s, d = -5.1 m (or y₀ = 5.1 m and y = 0) and a = -g = -9.8 m/s² for free fall. v and a are negative as they point downwards.

You can use the equation of motion 2ad = v² - v₀² to solve for v (remember d = y-y₀)

or v = sqrt(2ad + v₀²) Take the negative square root as the answer. (Note that 2ad will be a positive term when you substitute in.

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