# A projectile is shot from the ground at a velocity of 4 m/s and at an angle of (pi)/2. How long will it take for the projectile to land?

$.8$ seconds
Since the projectile is being shot from he ground at a 90 degree angle, we know it will travel straight up. Thus we can use the formula; Displacement=$.5 \left(- 10\right) {t}^{2} + 4 t$. -10 is used because that is the gravitational constant of earth, and is negative because the projectile Is accelerating downwards.
Now that we have this, we can simplify it to Displacement=$- 5 {t}^{2} + 4 t$. We want to find out when Displacement is 0, as this will give us the time it takes to hit the ground. To get the 0, factor out our equation. Factoring this out, we get $t \left(5 t - 4\right)$. Solving for 0, we get $t = 0 , .8$. We can rule out 0, since that is our starting time and point of origin, so the answer is .8 seconds.