You throw a 18.0 N rock into the air from ground level and observe that, when it

Question

You throw a 18.0 N rock into the air from ground level and observe that, when it is 15.0 m high, it is traveling upward at 18.0 m/s. A) Use the work-energy principle to find the rock's speed just as it left the ground. B)Use the work-energy principle to find the maximum height the rock will reach.

Explanation / Answer

(a) work done by gravity = change in K.E => -mgh = m(v2^2 - v1^2)/2 where v1 and v2 are velocities at starting and at the h point respectively. => v1 = 24.85 m/s. (b) let H be the max height => work done by gravity = change in K.E => -mgH = m(v2^2 - v1^2)/2 at max height v2 = 0 => H = v1^2/2g = 31.53 m

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