Physics 20-1 Final Review: Projectiles

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Homework Help Overview

The problem involves projectile motion, where a student throws an object from the top of a 75 m tall building at an initial speed of 16 m/s and an angle of 25 degrees above the horizontal. The objective is to determine how far from the base of the building the object will land.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss breaking the motion into horizontal and vertical components, questioning the setup of the problem, and calculating the time to reach maximum height. There are attempts to clarify the correct use of initial velocity components and the reference point for height.

Discussion Status

The discussion is ongoing, with participants providing insights into the calculations needed for time to maximum height and the implications of the chosen reference point. There is no clear consensus yet, as some participants continue to struggle with the calculations.

Contextual Notes

Participants are exploring the implications of different reference points for height and the correct application of kinematic equations in the context of projectile motion. There is an emphasis on ensuring the correct vertical component of velocity is used in calculations.

physicznoob
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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 = vit + 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.
 
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What do you get for the time to max height?
 
a = v2 - v1 / t
t = v2 - v1/ a
t = 0 - 16 / -9.81
t = 1.63 s.
 
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.
 
i still get the wrong answer...
 
where are u setting your zero? the top of the building or the bottom?
 
huh? if you mean velocity wise, at the top for vertical motion.
 
physicznoob said:
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.
 

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