A classical mechanics problem

Classical Mechanics Level 3

A Physics student stands on a ladder 12 feet above the ground and throws a ball up into the air. If it takes the ball 4.2 seconds to hit the ground, what was the ball's initial velocity in ft/s.

64 69 41 17.8

Connor Switala by Connor Switala , 21, USA

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1 solution

Connor Switala
Dec 5, 2016
  • Δ X = V o T + 1 2 a t 2 \Delta X = V_oT + {{1} \over {2}} at^2
  • − 12 = ( x ) ( 4.2 ) + ( 1 2 ) ( 32 ) ( 4.2 × 4.2 ) -12 = (x)(4.2) + ({{1} \over {2}}) (32)(4.2 \times 4.2)
  • − 12 = ( x ) ( 4.5 ) + ( − 282.24 ) -12 = (x)(4.5) + (-282.24)
  • − 12 f t + ( 16 f t / s e c ) ( 4.2 s e c ) 4.2 s e c = 64 f t / s e c \frac{-12ft + (16 ft/sec)(4.2 sec)}{4.2 sec} = 64 ft/sec
  • 64 is the answer.
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