A rock is thrown from the top edge of a 100-ft tall building at some unknown ang

Question

A rock is thrown from the top edge of a 100-ft tall building at some unknown angle above the horizontal. The rock strikes the ground a horizontal distance of 160 ft from the base of the building 5.0 s after being thrown. Assume that the ground is level and that the side of the building is vertical. Determine the speed with which the rock was thrown. [Hint: Choose an origin of coordinates and decide which directions are positive. Use a constant-acceleration equation for the x and y directions separately. Solve them to find the components of the initial velocity and hence the speed. You do not need to solve for the angle (although you can).]

Explanation / Answer

x-direction 160ft/5s = 32 ft/s

y-direction: d=d0 + vt + 1/2 gt^2==> -100=0 + v(5) + (-16)(5)^2 or v=+60 ft/s.

constructing a vector triangle V^2=(Vx)^2 + (Vy)^2 and tan @= 60/32

68 ft/s at an angle of 61.9 degrees

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