Monday, November 5, 2007

Look Out Below!

In class we were trying to work on this problem.

Maxine sees a pillow falling from her window. She know the pillow is falling at an acceleration of 20 ft / sec^2. She also knows that the pillow is traveling at an instantaneous speed of 30 ft/sec when Maxine saw it.

1. What is the instantaneous speed of the pillow 1 second AFTER Maxine saw it? 2 seconds after Maxine saw it?

2. What is the average speed of the pillow for the first 2 seconds AFTER Maxine saw it?

3. How far did the pillow fall during the first 2 seconds after Maxine saw it?

Maxine knows the sidewalk is 200 feet below her window.

4. How long did it take for the pillow to reach the ground from the time Maxine saw it?

5. Find a general expressions for the height of the pillow t seconds after Maxine saw it.

Please post your answers, questions, suggestions in the comments.

26 comments:

Andrew said...

nice way to put it, but a pillow is light, and that it wouldn't fly far.

Kendra Chapman said...

Well...my issue is finding the general equation. I think I solved for everything else correctly....I think. How do find the general expression??????

Mr. Marti said...

kendra,
what are your answers?

christina richards said...

1. i said after one second the pillow would be 20ft/second, and after 2 seconds it would be 40ft/sec.
2. i said 20ft/sec.
3. 40ft.
4. I was so confused, but i guessed and said 6.6 seconds.
5. h=20(t)

David C. said...

123 we did in class, so #4: 8.5, #5 (T*20)+30, I think

JULIANA Q said...

ok so @ first i completely diregarded the instantaneous speed of 30ft/sec after maxine saw the pillow but then i was enlightened by my class mates. im not too confident about these answers & the problem as a whole but heres what i got:
1)* 50ft/sec
*70ft/sec
2)60ft???
3)70
4)???? i think u do the triangle, height would be 200 hypotenuse 70, then we can figure out angle opposite of 90 degree angle.

Carlos O said...

1. 50ft/s and 70ft/s
2. 35ft/s
3. 100 ft
4. I didn't understand it too well, but I guessed around 3.3s
5. Again, I didn't understand it so i did t= (square root of (h/16))

Kendra Chapman said...

1. 20 ft per second and 40 ft per sec
2. 20 ft per second
3. 40 ft
-I was confused on 4 and 5

Carlos M. said...

1. 50 ft/s and 70 ft/s
2.60 ft/s
3.120 ft.
4. around 2.9 sec
5. 60f=n

Mr. Marti said...

carlos m,

I am interested in how you got your answer for #2. You said at 1 sec, the instant. speed is 50 ft/s and at 2 seconds, the instant. speed is 70ft/s. The pillow was initially going 30 ft/s. How do you get the average speed to be 60 ft/s? Just curious....

Javier said...

i was confused 4 problem 4 as well n got 6 sec.

Joey I. said...

Well, i was planning on leving a note, but i accidentlly left my notebook at achool.

Too bad, cuz I had all the answers...sorry guys...and girls
:-)

Natasha said...

1.) For 1 sec I got 50. For 2 sec, I got 70.

2.) The average speed was 60 (i think)

3.) The distance traveled was 120 ft.

4.) I wasn't sure how to do this one.

5.) I started it off as (1/2) (t) but I'm not sure it that's right or how to finish it off.

Carlos M. said...

I got that because the pillow was initially going 30 ft/s and 20ft/s after that so it's 50. Then after another sec you add 20 and get 70.

For the second Q. I added 50 and 70 to get 120. Then i divided it by 2 to get 60.

Mr. Marti said...

Carlos and anyone else that got 60 ft/s as their average speed....

I understand you got it by taking the average of 50 ft/s and 70 ft/sec. But....from time 0 to 1 sec, the pillow was moving. It wasn't going 50 ft/s until time was 1 second.

Could the average speed of the pillow for the first 2 seconds -- starting from time 0 -- be 60 ft/s?

Deloris M. said...

1.) After 1 second its going 50. For 2 seconds, 70.
2.)The average speed was 25 ft/sec.....(20 ft/sec +30 ft/sec^2)/2
3.)Distance after 2 sec...120 ft. How? (50 ft/sec^2)(2)
4.)It took the pillow 20 seconds
5.)h=50 ft/sec^2 (t)

Courtney Cole said...

I actually liked this problem set!
I was onnly confused on #5, because although I tried, I am not very sure of the equation that I created. The answers that I found are as follows:

1.) After the 1st second, it is 30 f/s
After 2 seconds it is 60 f/s
2.) The average speed is 45 f/s
3.)After the first two seconds, the pillow has traveled 60 feet.
4.) 6.7 seconds
5.)Height of Pillow= 200 feet- Amount of feet/sec travled

Kristen J said...

I'm not sure about the answers at all but I think that Deloris' answer for #5 is wrong just because if you multiple feet/seconds squared by seconds you get feet per second, which is not the unit for height we're using. Other than that I guess I agree with them. I don't have my answers to post.

morgan said...

Was I jsut me or were these problems too easy? I probably did them wrong, or am i getting my genius back?
1.(was it just me or did the problem ask a sec after he saw it and he saw it on the 1 sec so wouldn't we be giving answeres for sec 2+3, I dont know maybe im over analyzing)1sec=30ft/s - 2sec=60ft/s
2. average is 45ft/s
3. 60ft
4. 200/30=6.67
5. I dont know but i think JULIANA is on the right track.

Anonymous said...

1. 50 ft. per sec for first sec
70 ft. per sec for second sec
2. 60 ft. per sec
3. 120 ft. per sec
4. 4 sec
5. I have no idea...i think that we did something like this before where the time increased each time...i just forgot how to do it...i know that you don't use power but i just can't figure out what it is

Sam Maxey said...

The one above is Sam Maxey...i just didnt know what i was doing and i dont have a google account

Alfonso Navarro said...

1. I believe it was 50 ft/sec 1 second after maxine saw it and 70 ft/sec 2 seconds after maxine saw it
2. I believe the average speed was 60 ft/sec
3. It fell 70 feet
4. 2.8 sec
5. no idea how to figure out an expression

NiTa' said...

1. 50 feet per sec
2. 60 feet per sec
3. 122.5 feet
4. about 4.49 secs i think
5. I didnt get a formula i just guess and checked

Anonymous said...

Well as the last person to comment for the night (really morning). I got the chance to read everyone else comments to understand their progress to solve the problem. Since I did not take notes because get was in group work, which as you see came back to bit me. Anyways I do remember that the for the 1st sec was 50, 2nd sec was 70. Q2) ave. speed is 60sec and the rest IDK. :)

But I do feel that you have to take in when Maxine seen the pillow fall.

Sara .V

Anonymous said...

Also what about AIR RESISTANCE???

Rachel said...

I got really confused with this problem, but I ended up with the same answers as Sara because the pillow, when falling, increases by 20... at least that's what I thought...