Help me study for my physics test tomorrow!

Freebase Dali · 02-07-2012, 08:18 PM

Nevermind, that's acceleration.

skaltezon · 02-07-2012, 08:24 PM

Quote:

Originally Posted by Freebase Dali

Well displacement is actually velocity over time (d = v/t) if I remember correctly, but that's one dimensional. The problem has both the x and y dimension, and is asking for the components of the vector, which the vector would be a diagonal line. I would need to figure out the x component and the y component that made the resultant vector.

I think Tuna's right with d = v * t .

Freebase Dali · 02-07-2012, 08:27 PM

Yea, I was thinking of Acceleration.

skaltezon · 02-07-2012, 08:40 PM

Well, the time from firing to impact is 175/25 = 7 secs.

Reaches apogee midway at 3.5 secs., where vertical velocity = 0.

What velocity will be exactly cancelled by gravity after 3.5 secs.?

skaltezon · 02-07-2012, 08:45 PM

I'm guessing (10meters/sec/sec)(3.5 sec.) = 35 meters per second.

Now you can calculate muzzle velocity.

midnight rain · 02-07-2012, 09:06 PM

Quote:

Originally Posted by Freebase Dali

Word. Ok. So I have the basics. Now, when doing 2 dimensional kinematics, that trig comes into play, but I also have to remember some formulas. I can put those on my phone, so I'm not worried too much about it, since my phone is also my calculator, which is allowed.

So, how would you guys go about solving something like this (taken from a homework problem):

A projectile is launched from and returns to ground level. Air resistance is absent. The horizontal range of the projectile is R = 175 m, and the horizontal component of the launch velocity is Vox = 25 m/s. Find the vertical component Voy of the launch velocity.

Alright man, I looked up 2 dimensional kinematics and I'm still not sure how to solve this problem. My best guess:

Using the equation: y=v*t+.5*a*t^2

where:
y = vertical displacement
v= velocity
t= time
a = acceleration

and figuring out that t=7

you have:

0 = v*7+.5*(-9.8)*7^2

which got me

v= 34.3 m/s

have no idea if that's actually right though

midnight rain · 02-07-2012, 09:19 PM

Ah cool just noticed you got the same answer, guess we're on the same page.

Freebase Dali · 02-07-2012, 09:28 PM

Quote:

Originally Posted by Tuna

Alright man, I looked up 2 dimensional kinematics and I'm still not sure how to solve this problem. My best guess:

Using the equation: y=v*t+.5*a*t^2

where:
y = vertical displacement
v= velocity
t= time
a = acceleration

and figuring out that t=7

you have:

0 = v*7+.5*(-9.8)*7^2

which got me

v= 34.3 m/s

have no idea if that's actually right though

Ah yes, that makes sense.
Seeing the equation written that way (instead of the way my professor wrote it) makes things a lot easier. It's just a matter of plug and play then.

midnight rain · 02-07-2012, 09:32 PM

Quote:

Originally Posted by Freebase Dali

Ah yes, that makes sense.
Seeing the equation written that way (instead of the way my professor wrote it) makes things a lot easier. It's just a matter of plug and play then.

Yeah which equation you use is really all dependent on what you're given in the first place.

Here's the list I got it from in case you don't have them all:

Horizontally Launched Projectile Problems

Freebase Dali · 02-07-2012, 09:35 PM

There are 4 of them that he said we'd need. Those I have typed into my phone. I don't have any with like Viy though... does that mean the initial velocity of Y, or is that the initial velocity multiplied by a number represented by Y?

02-07-2012, 08:18 PM	#21 (permalink)
Freebase Dali Partying on the inside Join Date: Mar 2009 Posts: 5,584	Nevermind, that's acceleration. __________________

02-07-2012, 08:27 PM	#23 (permalink)
Freebase Dali Partying on the inside Join Date: Mar 2009 Posts: 5,584	Yea, I was thinking of Acceleration. __________________

02-07-2012, 08:40 PM	#24 (permalink)
skaltezon Music Addict Join Date: Nov 2010 Location: hairball cluster Posts: 326	Well, the time from firing to impact is 175/25 = 7 secs. Reaches apogee midway at 3.5 secs., where vertical velocity = 0. What velocity will be exactly cancelled by gravity after 3.5 secs.? __________________ . . . Occupy protest locations in the United States Occupy protest locations worldwide

02-07-2012, 08:45 PM	#25 (permalink)
skaltezon Music Addict Join Date: Nov 2010 Location: hairball cluster Posts: 326	I'm guessing (10meters/sec/sec)(3.5 sec.) = 35 meters per second. Now you can calculate muzzle velocity. __________________ . . . Occupy protest locations in the United States Occupy protest locations worldwide

02-07-2012, 09:35 PM	#30 (permalink)
Freebase Dali Partying on the inside Join Date: Mar 2009 Posts: 5,584	There are 4 of them that he said we'd need. Those I have typed into my phone. I don't have any with like Viy though... does that mean the initial velocity of Y, or is that the initial velocity multiplied by a number represented by Y? __________________

02-07-2012, 09:19 PM	#27 (permalink)
midnight rain Music Addict Join Date: Mar 2009 Posts: 1,711	Ah cool just noticed you got the same answer, guess we're on the same page.