Physics problem, How fast are the pebbles going when they hit her window?

Question

Romeo is chucking pebbles gently up to Juilet's window, and he want the pebbles to hit the window with only a horizontal component of velocity. He is standing at the edge of a rose gardern 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?


I know that to make the pebble have no vertical velocity it must be at its apex, and there fore the maximum height of the pebble's prejected path is 5 meters and its range is 10 metes, but how do I solve the problem from there? I have no initial velocity (or any form of velocity for that matter), no angle of release, and no amount of time that it take to either hit the window or go the full range. Please help! Thanks soo much.

P.S. and explination on how to recieve the answer is 4000x better than just the anwer.

Sarah

Answer 1

We know that, for the vertical component of the pebble's motion: 4.5=-0.5*9.8*T^2+VoT

because there is no vertical motion at the apex, v0=9.8T

Substituting: 4.5=4.9T^2

Solving: T=.958 Seconds

Given that the pebble has traveled precisely 5 m in T, the horizontal component of the velocity is 5/.958 or 5.22 m/s.

Answer 2

let T seconds be the time a pebble takes to get to its apex. Then in time T the pebble has to travel a horizontal distance of 5.0 meters (assuming the window is flush with the outside wall). That means the horizontal velocity has to be 5/T m/s.



To find T, use the formula for constant linear acceleration:



D = Vi T + (1/2) A (T^2)



D is the vertical distance

A is the acceleration (about 9.8 m/s^2)



Since time going up is time going down, you can assume Vi (the initial velocity) is 0. So T is the only unknown in this quadratic equation.

Answer 3

to respond to this concern you want: initial vertical % (vf^2=vi^2+2ad) --> -vi^2=2ad Time it takes for the rock to hit the window (vf=vi + at) --> (vf-vi)/a=t then you definitely can plug interior the area and time to get the speed So 0=vi^2+2(-9.8m/s^2)(4.5) = 9.3914m/s Then locate time utilizing new vi (-9.3914m/s)/(-9.8m/s^2)= .9583s finally, to get your speed of the rock hitting the window you do x=vt 5m(horizontal distance)= 5.217m/s