Physics Homework

Question

A student standing on the ground throws a ball straight up. The ball leaves the students hand with a speed of 15 m/s when the hand is 2.0 m above the ground. How long is the ball in the air before it hits the ground? (The student moves her hand out of the way.)

Answer 1

Start with the time required to get to the highest point. At this time the velocity is 0. The velocity is a function of time and the gravitational acceleration (g)

v₁ - v₂ = g*t

15 - 0 = 9.8t

t = 15 / 9.8 seconds

The distance travelled in this period is t times the average velocity, which is 15 / 2

d = 15/2 * 15/9,8 = 225/19.6 = 11.5

the final height is d + 2 = 13.5

Finally use the free-fall equation to get the time: d = 1/2 * g * t²

13.5 = 9.8/2 * t²

Solve this for t