A ball A is thrown vertically upward from the top of a 28-m-high building with a

Question

A ball A is thrown vertically upward from the top of a 28-m-high building with an initial velocity of 4 m/s. At the same instant another ball B is thrown upward from the ground with an initial velocity of 20 m/s. Part A Determine the height from the ground at which they pass. Express your answer to three significant figures and include the appropriate units hValue Units Submit Request Answer Part B Determine the time at which they pass Express your answer to three significant figures and include the appropriate units HA tValue Units Submit Request Answer

Explanation / Answer

given ball A is thrown vertically upwards from the top of a h = 28 m tall building

u = 4 m/s

another ball thrown from the ground, u' = 20 m/s

a. let say they pass at height y

then

y = u'*t - 0.5*gt^2

y - h = u*t - 0.5*gt^2

hence

u'*t - 0.5gt^2 - h = ut - 0.5gt^2

u'*t - ut = h

t = h/(u' - u) = 28/16

hence

y = 20*28/16 - 0.5g*28^2/16^2 = 19.9784375 m

b. t = 28/16 = 1.75 s

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