Why Am I Struggling with Projectile Motion Problems in Physics?

[HurricaneH]

Help:(

1) A firefighter, 50m away froma building, directs a hose at an angle of 30*, if the initial speed of the stream is 40m/s, what height does it hit the building?

i'm guessing i make a triangle and solve for h

tan30= h/50, solve for h, i get 28 m

...but it's not the right answer, what am i doing wrong?

2) A rifle is aimed horizontally at the center of a large target 200m away. The initial speed of the bullet is 500m/s. A) Where does the bullet strike the target? B) What angle above the line of sight should the rifle be to hit the target?

I don't know what equation to use:(

 

[arildno]

1) Why do you think the water will flow as a STRAIGHT line??
It does not; it follows the parabola given by ordinary projectile motion
2)Similarly here
3)Don't double post

 

[HurricaneH]

ugh, should have been obvious:(

so i would have to find t, using the equation X=Xxo+Voxt+1/2axt*2

50=40t + 4.9t^2

solve for t using the quadratic equation

then plug in t into Y=Yyo+ Voyt+1/2ayt^2

Yyo= o
Voy=20
a= 9.81