Practice!

Sample Problem

Jason throws a ball horizontally off a 300. meter cliff at 15.0 m/s. How long will it travel before it hits the ground? Use significant figures, and estimate g to be equal to 9.81 m/s². Round the answer to the nearest hundredth.

Solution

Use the formula dy = v0y t + 1/2 at2 to solve for time. We know the vertical distance x, as well as the initial vertical velocity, which is zero, since the object was thrown horizontally.

We know that acceleration (a) is, in this case, g, or 9.81 m/s2.

We can substitute all the values in, so the new formula is 300 = 0 + 1/2 (9.81) t2.

We can now isolate for t so 300 (2) /9.81 = t2, and t = √ (300 (2) /9.81) .

Computing this, we get that the object will hit the ground in t ≈ 7.82 seconds