Watching Through The Window

Classical Mechanics Level 2

A boy spots a ball that goes up past an open window. The ball, which passes very close to the window, is in view of the boy for 0.25 s while going up, and the top-to-bottom height of the window is 2.0 m. What is the ball’s upward velocity at the bottom of the window? (Take g = 10 m/s2)

9.25 m/s 8.00 m/s 8.575 m/s 18.75 m/s

Sanjay Balaji by Sanjay Balaji , 21, India

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7 solutions

Sanjay Balaji
Apr 7, 2014

s=ut + 1/2 at^2. 2 = u * 1/4 - 1/2 *10 *1/16. u=9.25 m/s.

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kinematics equation just replace a = g, as given g= 10ms^(-2),

by applying s = ut - 0.5gt^(2),

2 = 0.25u - 0.5(10)(0.25)^(2)

u = (2 + 0.3125) / ( 0.25)

u = 9.25 m/s

Mayank Chaurasia - 7 years, 1 month ago

x=v.t-(1/2 g t*t)

Bahaa Salah - 7 years, 1 month ago

u = average velocity + gt/2 = 8 + 1.25 = 9.25

proof :

1(u3=final velocity)-----

u - gt

2(u2)----- (middle point of 1 and 3) average velocity= u2 = u - gt/2

u-gt/2

3-----u(initial velocity)

Piyush Yadav - 7 years, 1 month ago

Its simple just use second law of motiom

Syed Faizan Husain - 7 years, 1 month ago

I did it that way many times but i get 6.75 every time

Aya Gad - 7 years, 1 month ago

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because you are taking positive value of 'g'. put g=-10

Pawankumar Pandey - 7 years, 1 month ago

D=si x 0.25 - 0.5 x 0.25 x 0.25 D=2 t=0.25

Solve si = 9.25 m per second

Samir Shaheen - 7 years, 1 month ago

s=ut+1/2at^2

Piyush Desai - 7 years, 1 month ago

as it is upwards(y axis motion),

by kinematics equation just replace a = g, as given g= 10ms^(-2),

by applying s = ut - 0.5gt^(2),

2 = 0.25u - 0.5(10)(0.25)^(2)

u = (2 + 0.3125) / ( 0.25)

u = 9.25 m/s....

thanks...

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Agus Faisal
Apr 27, 2014

h = vo.t + 1/2.g.t^2 2 = vo . 0,25 + 1/2 . 10 . (0,25)^2 32/16 - 5/16 = 1/4 . vo (27/16) . 4 = vo 27/4 = vo

vt = vo + g.t vt = 27/4 + 10 . 0,25 vt = 27/4 + 10/4 vt = 37/4 vt = 9,25 m/s

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S = ut + 1/2 at^2 . Solve by this

Kavita Thakur - 7 years, 1 month ago
Rushi Chhatrala
Apr 26, 2014

answer :9.25. use s=ut+0.5at^2

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Ghulam Murtaza
Apr 21, 2014

s=ut + 1/2 at^2. 2 = u * 1/4 - 1/2 *10 *1/16. u=9.25 m/s.

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Vishmay Patel
Apr 17, 2014

s=ut + 1/2 at^2. 2 = u * 1/4 - 1/2 *10 *1/16. u=9.25 m/s.

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Stefan Brajkovski
Apr 15, 2014

X=V(at the bottom) t - (a t^2)/2 ====> V= (2x + g*t^2)/2t

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