Homework Help v1.3

[ames3]

the normal is a line perpendicular to the tangent at hte same point, so after u find the slope of the tangent, do the negative reciprocal.

[pkzild]

ohhh ya!

normal of (a, b) = (-b, a)

[Ice(v)an]

what does spirftastic mean?

[Denny Crane]

doesnt sound like a real word
dictionary.com doesnt have it on its database

[batman555]

Naruto|Parker, did you spell it right?

[Ice(v)an]

I know ^^ my friend just used it in a sentence..well sort of.. well I'm spiftastic... whatever that means?

[Denny Crane]

its a made up word
probably having something to do with spiffy
do you know how to take words into context. that sounds so slang it is not funny. try to keep this thread to stuff that is actually worth helping on. you've already been banned once for asking for too much help. so try and reduce the amount of questions asked

[Ice(v)an]

I know...

I just thought that was a word.. I didn't mean to piss people off again ad2:

[Raug]

Quick question...

s(t)'s derivative is v(t) and v(t)'s derivative is a(t) right?

s being distance, v being velocity and a being acceleration


Say, given a problem such as this:

A ball is thrown directly upward at a speed of 64 ft/s from a cliff 80ft above the ground. THe acceleration due to lunar gravity is 5.2 ft/s^2

A. Find the expression for the velocity and height of the ball t seconds after it is released.

B. At what time does the ball reach its highest point? What is the maximum height?

C. When does the ball strike the ground at the base of the cliff? What is the velocity at that instant?




All I basically want is a kind of explination of how to do the steps. I kind of get the basic idea, but get kind of lost on the "how" part.

[ames3]

well he gave the acceleration is 5.2ft so if u integrate the acceleration u get v(t) and u integrate v(t) to get s(t)....(sorry)

[Raug]

Yeah, well I just tried to do that and got


a(t) = dv/dt = -5.2
v(t) = -5.2t + C ---> v(0) = 64 ---> v(t) = -5.2 + 64
s(t) = (-5.2/2)t^2 + 64t + D ---> s(0) = 80 ---> s(t) = (-5.2/2)t^2 + 64t + 80

Now, using those formulas I tried to do part B.

Since I want to find the time at which the ball reaches its highest point I did this:

v(t) = 0 (since the derivative of the distance is time and when v(t) = 0 I think it's supposed to be either a maximum or minimum)

0 = -5.2t + 64
t = 12.31

Now from that I don't exactly know how to get the height itself...do I just plug it back into s(t)?

[batman555]

Originally Posted by Zarael

s(t)'s derivative is v(t) and v(t)'s derivative is a(t) right?

Correct.

Originally Posted by Zarael

A ball is thrown directly upward at a speed of 64 ft/s from a cliff 80ft above the ground. THe acceleration due to lunar gravity is 5.2 ft/s^2

A. Find the expression for the velocity and height of the ball t seconds after it is released.

I'm too lazy to look in my physics book, but there should be some kinematic equations in your text. Just apply them to your problem. Depending on where you draw your arbitrary coordinate system, y(initial) could either be at 0 or at 80. Therefore, your y(final) will either be at -80 or 0.

Originally Posted by Zarael

B. At what time does the ball reach its highest point? What is the maximum height?

At the highest point, the velocity is zero, so plug that into your expression and solve for t. To get the maximum height, take the derivative of your expression, set it equal to 0, and I think you use the t from before to plug in to get the maximum height. (Whenever you're asked for the maximums and minimums, that should be a clue for you to differentiate and set equal to zero.)

Originally Posted by Zarael

C. When does the ball strike the ground at the base of the cliff? What is the velocity at that instant?

Set your y(final) equal to however you drew your coordinate system and solve for t. Using that t and y(final), plug it into another kinematic equation to solve for velocity.

[ames3]

thanks bat=D

[batman555]

Originally Posted by Zarael

t = 12.31

Now from that I don't exactly know how to get the height itself...do I just plug it back into s(t)?

Well, height is a position. 'S' is a position. I don't see why not.

Sorry about my explanation earlier. I guess it didn't help much.

[Raug]

Hey you took the time to write all that out so I appreciate it.

Thanks

[canza]

Ummmm can someone help me?

Solid silver carbonate decomposes to produce silver metal,oxygen gas, and carbon dioxide.

Can someone help me write this balanced equation out?

Oh and after that can someone show me how to do this:
What mass of silver will be produced by the decomposition of 6.32 g. silver carbonate?

[pkzild]

isnt it just

2Ag2CO3 --> 4Ag + O2 + 2CO2

[canza]

o...thx!!