Answer:
6.7 m/s
Explanation:
If the pebbles have only a horizontal component when they hit the window, then the vertical component is 0, meaning the pebbles are at the highest point of their trajectory.
In the y direction:
y = yā + vt ā Ā½ atĀ²
8.0 m = 0 m + (0 m/s) t ā Ā½ (-9.8 m/sĀ²) tĀ²
8.0 m = 4.9 m/sĀ² tĀ²
t = 1.28 s
In the x direction:
x = xā + vā t + Ā½ atĀ²
8.5 m = 0 m + vā (1.28 s) + Ā½ (0 m/sĀ²) (1.28 s)Ā²
8.5 m = 1.28 s vā
vā = 6.65 m/s
Rounded to two significant figures, the pebbles are moving 6.7 m/s when they hit the window.
