A projectile is launched horizontally with the speed of 80 m/s. If the projectile is launched 1.5 m above the floor how long does it take the projectile.....

Question

....to hit the floor?

 

Test tomorrow and I'm not sure on how to work out the equations. Any help would be appreciated. Thanks!

Answer 1

Grace,

The key here is that the projectile is launched horizontally, and therefore has an initial vertical velocity component of 0. All you need to figure out is how long does it take for anything to fall 1.5m from a resting position. The 80 m/s is only important if you want to know where it will hit the floor. It has no effect on this problem. The equation we might be drawn to is the basic Newtonian equation:

 

h_f = v₀t + (a/2)t² + h₀

 

where h is height, v is velocity, and a is acceleration. In some cases, it would be a pain to solve this for t; but since

v₀ = 0, this one is easy.

 

0 = (-9.8/2)t² + 1.5

-1.5 = -4.9t²

-1.5/-4.9 = t²

0.55 s = t