Question #4450

Romeo is chuckling pebbles gently up to Juliets window, and he wants the pebbles to hit the window with only a horizontal component of velocity. He is standing at the edge of a rose garden 4.5 m below her window and 5.0 m from the base of the wall. How fast are the pebbles going when they hit her window?

Expert's answer

Suppose the pebble had initial velocities Vx and Vy (V=sqrt(Vx^2+Vy^2)). As pebbles hit the window with only a horizontal component of velocity Vx, so

the vertical component becomes equal to zero while the pebble is in the air.

Let’s find this time t from the equation for vertical displacement:

H = 4.5 = (gt^2)/2 => t = 3/sqrt(g).

The equation for horizontal displacement is:

S = 5 = Vx*t => Vx = 5/t = 5*sqrt(g)/3 = 5*sqrt(9.8)/3 = 5.22 m/s.

So, Vx = 5.22 m/s.

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