Physics 20-1 Final Review: Projectiles

[physicznoob]

Homework Statement

A student is standing on the top of a building and he throws an object into the air with a speed of 16 m/s at an angle of 25 degrees above the horizontal. If the building is 75 m tall, how far from the base of the building will the object hit the ground?

Homework Equations

v = d/t
d = v_it + 1/2at²

The Attempt at a Solution

i tried to break it up into horizontal and vertical components and break it down into speed, then distance, then time. but nothing i do seems to work.

 

[LowlyPion]

What do you get for the time to max height?

 

[physicznoob]

a = v2 - v1 / t
t = v2 - v1/ a
t = 0 - 16 / -9.81
t = 1.63 s.

 

[LowlyPion]

There's your problem right there.

The vertical component of velocity is what must be taken to determine time to max height.

That is 16*sin25.

The horizontal component is 16*cos25.

 

[physicznoob]

i still get the wrong answer...

 

[KMjuniormint5]

where are u setting your zero? the top of the building or the bottom?

 

[physicznoob]

huh? if you mean velocity wise, at the top for vertical motion.

 

[LowlyPion]

i still get the wrong answer...

So what is your time to max height?

You know that must be 16*Sin25/g = t

And how high is that from launch? y = 1/2 g*t²

Now it is a simple free fall problem to determine the time to hit the ground isn't it?

With the total time ... and the horizontal component of velocity ... viola your distance along the ground.