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 = y₀ + vt − ½ at²
8.0 m = 0 m + (0 m/s) t − ½ (-9.8 m/s²) t²
8.0 m = 4.9 m/s² t²
t = 1.28 s
In the x direction:
x = x₀ + v₀ t + ½ at²
8.5 m = 0 m + v₀ (1.28 s) + ½ (0 m/s²) (1.28 s)²
8.5 m = 1.28 s v₀
v₀ = 6.65 m/s
Rounded to two significant figures, the pebbles are moving 6.7 m/s when they hit the window.
