Assuming no air resistance, how long does it take a penny to fall if thrown down with an initial velocity of 5.0 m/s from the CN tower (553m). Acceleration due to gravity is 9.8 m/s2?

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Answer 1 · 2015-06-12T14:17:59

#t~=10.1s#.

First of all, I suppose that the velocity is a vertical velocity downward.

The motion is an accelerated one with the law:

#s=s_0+v_0t+1/2g t^2#;

so, assuming the origin of the motion up on the tower:

#553=0+5t+0.5*9.8*t^2rArr#

#4.9t^2+5t-553=0#

#Delta=b^2-4ac=25-4*4.9*(-553)~=104^2#

#t=(-b+-sqrtDelta)/(2a)=(-5+-104)/(2*4.9)#

#t_1~=(-5-104)/9.8<0# not acceptable,

#t_2~=(-5+104)/9.8~=10.1s#.