# A projectile is shot from the ground at a velocity of #1 m/s# and at an angle of #(7pi)/12#. How long will it take for the projectile to land?

##### 1 Answer

0.198 seconds

#### Explanation:

The key part of this problem to understand is that it is only the vertical motion of the projectile which matters; assuming the ground is perfectly flat (and not sloped), the horizontal motion only affects how far away from you it lands, not how long it takes to land.

To find the initial vertical velocity, we use the sine trigonometric function according to this formula:

Our initial velocity is

As you can see, this vertical velocity is nearly the full initial velocity. This is reasonable, as

Now, there are 2 ways to proceed at this point. One way uses the common position formula

The other way is to exploit the symmetry of vertical motion under constant acceleration of gravity with no other factors (wind resistance, etc). We know the projectile is going upwards with an initial vertical velocity of

Use the common velocity formula, with

It will take 0.099 seconds to stop rising, which means it'll take another 0.099 seconds to fall back down, for a total time in the air of 0.198 s.

**Alternative**

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