A classical mechanics problem by Daniel Yang

Classical Mechanics Level 2

A baseball pitcher throws two baseballs simultaneously from a height of 60 60 m. One is thrown up with the speed of x x m/s and the other is thrown down with x x m/s. What is the difference in the time it takes for the balls to reach the ground?

sqrt(x/g) sqrt(60/x^2) x/g 2x/g

Daniel Yang by Daniel Yang , 21, USA

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1 solution

Daniel Yang
Sep 11, 2014

Because the flight of a projectile is parabolic and vup=vdown, the only difference in the time is the time of fly(the time it takes the upward thrown to get to the same elevation as the building). The answer is, therefore, 2vo/g or 2x/g.

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what about the acceleration of gravity

John Zhou - 5 years, 8 months ago

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ok. So the graph of a projectile is a parabola. Assume that there is a plane at height 60m. that goes on to infinity. The projectile that is launched up hits the plane with the same velocity as the rock going down. Thus, the rest of the motion is the same and takes the same exact time. The time of fly of a projectile that lands in the exact height it starts in is 2v {0y}/g where g is the acceleration due to gravity and v {0y} is the y component of the velocity. However, since the motion is vertical, the y component of the motion is v. Thus, the answers is 2v/g. Btw, the acceleration due to gravity is g or -9.81m/s^2

Daniel Yang - 5 years, 8 months ago

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