# What is hang time?

1. Mar 19, 2010

### ThetaPi

Could someone kindly explain to me what hang time is, in the context of 2D projectile motion? Enlighten me on the equations of motion that might be applicable to such a problem.

In other words, given a projectile launched at $$\theta$$ above the horizontal with an initial velocity of $$v_0$$, how do we calculate the hang time?

Thoughts. We need to calculate the time it takes for the projectile to reach the maximum height of the trajectory ($$t_1$$), and the time it takes to hit the ground after attaining its maximum height ($$t_2$$), and then add up $$t_1+t_2$$. I think that it will be convenient to use the y-component of $$v_0$$.

The maximum height of the trajectory is $$|1/2gt_2^2|$$. We can use this in the equation $$s_y=v_{0y}t_1-1/2gt_1^2$$ to find $$t_1$$.

I am rather confused...some posts I saw while browsing the forums said that the initial velocity does not affect the "hang time".

Thank you
TS

Last edited: Mar 19, 2010
2. Mar 19, 2010

### dacruick

velocity in the x-direction doesn't have an affect on hang time. hang time to me is simply the time that the projectile is in the air.

3. Mar 19, 2010

### ThetaPi

I know that, but how do we calculate that numerically?

I presume that hang time is dependent on the y-component of the initial velocity?

Thanks again.

4. Mar 19, 2010

### dacruick

right. you've written the equation that is going to give you the answer. If it is a projectile starting and stopping at the same y value, you know that maximum height has to be at half the total time its in the air. try working through it you seem to understand the concept