A student at the top of a building which eight is 50.0 meter throws a red ball u

Question

A student at the top of a building which eight is 50.0 meter throws a red ball upward with speed 20.0 m/s and simultaneously throws a blue ball downward with the same initial speed 20.00 m/s. Questions: a) how low takes red ball to hit the ground? What is its touch-down velocity? b) How long takes blue ball to hit the ground? What is its touch-down velocity? c) if there is yellow ball at same time free fall from the top of the building, how long it takes yellow ball to hit ground? What is its touch- down velocity?

Explanation / Answer

here,

height , h = 50 m

for the red ball

the initial velocity , u = - 20 m/s

let the time taken to hit the ground be t

h = u * t + 0.5 * g * t^2

50 = - 20 * t + 0.5 * 9.8 * t^2

t = 5.83 s

the time taken to hit the ground is 5.83 s

the final velocity , v = - 20 + g * t

v = - 20 + 9.8 * 5.83 = 37.1 m/s

for the blue ball

the initial velocity , u = 20 m/s

let the time taken to hit the ground be t

h = u * t + 0.5 * g * t^2

50 = 20 * t + 0.5 * 9.8 * t^2

t = 1.74 s

the time taken to hit the ground is 1.74 s

the final velocity , v = 20 + g * t

v = 20 + 9.8 * 1.74 = 37.1 m/s

for the green ball

the initial velocity , u = 0 m/s

let the time taken to hit the ground be t

h = u * t + 0.5 * g * t^2

50 = 0 * t + 0.5 * 9.8 * t^2

t = 3.19 s

the time taken to hit the ground is 3.19 s

the final velocity , v = 0 + g * t

v = 0 + 9.8 * 3.19 = 31.3 m/s

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