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Wednesday, September 12, 2012

Q.432. Vertical motion under gravity.

Question 432.
An object is thrown downward with an initial speed of 6 m/s from a height of 42 m above the ground. At the same instant, a second object is propelled vertically up from ground level with a speed of 55 m/s. At what height above the ground will the two objects pass each other?

Answer 432.
Let h = height above the ground where they pass each other.
=> 42 - h = 6t + 4.95t^2
and h = 55t - 4.95t^2
Adding,
42 = 61 t
=> t = 42/61
Plugging this value of t in h = 55t - 4.95t^2
=> h
= 55 * (42/61) - 4.95 * (42/61)^2
= 37.87 - 2.35
= 35.52 m.

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