# How long in the air

A projectile is launched off a click at an angle. The cliff is 15m high, the projectile is launched at 25 degrees above horizontal. How much time is the projectile in the air before hitting the ground?

To solve this problem, start by breaking the motion of the projectile into horizontal and vertical components. The projectile’s velocity has both an upward and forward component because it is launched at an angle. The time the projectile spends in the air depends on how long it takes for the vertical component of its motion to bring it back down to the ground after being launched off the cliff.

You need to calculate how long it takes for the projectile to rise, stop, and then fall back down past the height of the cliff. The height of the cliff (15 meters) means the projectile has to fall this distance in addition to its downward motion from the highest point it reaches. Using the initial vertical velocity and acceleration due to gravity, you can determine the total time the projectile remains in the air before it hits the ground.

## Related Problems

A ball is thrown off a building. If the ball is thrown up at 5 m/s and lands 3 seconds later

Find the height of the building

Find the impact velocity of the ball

A key falls from a bridge that is 45 m above the water. It falls directly onto a model boat moving with constant velocity that is 12 m in front of the point of impact when the key is released. What is the speed of the boat?

A swimmer is capable of swimming 0.60 ni/s in still water. (a) If she aims her body directly across a 55-m-wide river whose current is 0.50 m/s, how far downstream (from a point opposite her starting point) will she land? (b) How long will it take her to reach the other side?

In a rescue attempt, a hovering helicopter drops a life preserver to a swimmer being swept downstream by a river current of a constant velocity v. The helicopter is at a height of 9.8 m. The swimmer is 6.0 m upstream from a point directly under the helicopter when the life preserver is released. It lands 2.0 m in front of the swimmer. How fast is the current flowing? Neglect air resistance.

13.7 m/s

9.8 m/s

6.3 m/s

2.8 m/s