soompi forums: Physics Help! - soompi forums

Jump to content

Page 1 of 1

Physics Help!

#1 User is offline   O0OITSTIFFANYY 

  • Member
  • Pip
  • Group: Members
  • Posts: 391
  • Joined: 13-June 06

Posted 30 September 2008 - 10:23 AM

I'm really bad at science, so please help me answer these questions! And if its not a bother please show me how you did it..

Equations:
v = d/t
a = [delta]v/t
Vf = Vi + at
d= Vit+1/2at^2
Vf^2 = Vi^2 + 2ad

v = average velocity
d = distance
t = time
a = acceleration
Vf = final velocity
Vi = initial velocity



Consider the plot below describing motion
along a straight line with an initial position of
x0 = 10 m.


What is the position at 2 seconds? Answer in
units of m.

What is the position at 6 seconds? Answer in
units of m.

What is the position at 9 seconds? Answer in
units of m.




I REALLY APPRECIATE THE HELP! THANK YOUU!!

Tiffany&Co's Store, Status, Requests, & Survey - featuring ADORABLE KOREAN NOTEBOOKS and CCT/YY ON-HAND ITEMS
0

#2 User is offline   xingjing 

  • 横顔の愛...
  • Icon
  • Group: Friends of Soompi
  • Posts: 2,002
  • Joined: 16-January 06

Posted 30 September 2008 - 05:33 PM

The key to this is understanding that as you integrate velocity with respect to time, you obtain a change in displacement. If you haven't taken calculus, don't worry - basically what I'm saying is that when you take the area under the graph of velocity vs. time, you obtain a net change in displacement.

Take part a for example. The area under the graph is a triangle, whose area is 1/2 * base * height or 1/2 * 2* 9 = 9. Thus the net change in displacement is +9. And since x= x0 + vt, then x = 10 + 9 (the net change in displacement you found from the graph, which is much like velocity times time). Thus, you should obtain an answer of x = 19 at t = 2.

Do the same for the other two parts. For part c, be careful - since the graph goes under the x-axis at time 6, just take the area between the graph and the x-axis as the area under the graph.

Was that clear? Sorry if it wasn't.


withs2 cb save darfur m.a.a.p
in love with 동방신기 and 빅뱅 and more

I have measured out my life with coffee spoons. - T.S. Eliot
0

#3 User is offline   O0OITSTIFFANYY 

  • Member
  • Pip
  • Group: Members
  • Posts: 391
  • Joined: 13-June 06

Posted 30 September 2008 - 07:43 PM

QUOTE (xingjing @ Sep 30 2008, 09:33 PM) <{POST_SNAPBACK}>
The key to this is understanding that as you integrate velocity with respect to time, you obtain a change in displacement. If you haven't taken calculus, don't worry - basically what I'm saying is that when you take the area under the graph of velocity vs. time, you obtain a net change in displacement.

Take part a for example. The area under the graph is a triangle, whose area is 1/2 * base * height or 1/2 * 2* 9 = 9. Thus the net change in displacement is +9. And since x= x0 + vt, then x = 10 + 9 (the net change in displacement you found from the graph, which is much like velocity times time). Thus, you should obtain an answer of x = 19 at t = 2.

Do the same for the other two parts. For part c, be careful - since the graph goes under the x-axis at time 6, just take the area between the graph and the x-axis as the area under the graph.

Was that clear? Sorry if it wasn't.


Thanks! I got the first two parts down but I still don't understand the third ..
Can someone help clarify how you do the third part?
Tiffany&Co's Store, Status, Requests, & Survey - featuring ADORABLE KOREAN NOTEBOOKS and CCT/YY ON-HAND ITEMS
0

#4 User is offline   joie.de.vivre 

  • "..the air in your lungs is there for a reason"
  • Pip
  • Group: Members
  • Posts: 1,987
  • Joined: 29-March 07

Posted 30 September 2008 - 08:06 PM

you subtract that triangular area from t=6 'til t=9 from the area under the graph from t=0 'til t=6.
because position is the antiderivative [you've learned calculus, yeah? it doesn't matter that much, anyway, here] of velocity
Our species is the only creative species, and it has only one creative instrument, the individual mind and spirit of a man...Posted Image
0

#5 User is offline   O0OITSTIFFANYY 

  • Member
  • Pip
  • Group: Members
  • Posts: 391
  • Joined: 13-June 06

Posted 01 October 2008 - 06:12 AM

QUOTE (laugh-cry-smile @ Oct 1 2008, 12:06 AM) <{POST_SNAPBACK}>
you subtract that triangular area from t=6 'til t=9 from the area under the graph from t=0 'til t=6.
because position is the antiderivative [you've learned calculus, yeah? it doesn't matter that much, anyway, here] of velocity


Is the answer 57?
I tried putting that answer, but the computer said it was wrong
Tiffany&Co's Store, Status, Requests, & Survey - featuring ADORABLE KOREAN NOTEBOOKS and CCT/YY ON-HAND ITEMS
0

#6 User is offline   joie.de.vivre 

  • "..the air in your lungs is there for a reason"
  • Pip
  • Group: Members
  • Posts: 1,987
  • Joined: 29-March 07

Posted 01 October 2008 - 06:10 PM

um is it 45 for c then?
(35+10)
Our species is the only creative species, and it has only one creative instrument, the individual mind and spirit of a man...Posted Image
0

#7 User is offline   xtah_ 

  • Member
  • Pip
  • Group: Banned
  • Posts: 109
  • Joined: 18-September 07

Posted 02 October 2008 - 01:06 AM

hint :
area under graph = distance travelled; do remember to +10m (initial position)
negative velocity = negative direction (meaning it gets closer to the initial position[t=0s] if its on the positive side)
0

Share this topic:


Page 1 of 1

2 User(s) are reading this topic
0 members, 2 guests, 0 anonymous users