Go Back   Physics Help Forum > High School and Pre-University Physics Help > Kinematics and Dynamics

Kinematics and Dynamics Kinematics and Dynamics Physics Help Forum

Reply
 
LinkBack Thread Tools Display Modes
Old Oct 19th 2008, 04:40 PM   #1
Junior Member
 
Join Date: Oct 2008
Posts: 2
Calculating average Acc at end of initial acc phase

Alright so here is the question: Using the formula Vf=Vi+(a)(t), calculate the velocity of the cars at the end of their initial average acceleration phase. Assume the acceleration is the average one you calculated above. Answer in m/s and km/h.


The average i calculated in the previous one is 4.4m/s or 15.8km/h


The biggest problem i have is the fact that velocity is a speed with the amount of distance you have travelled calculated in there.

Last edited by simplekin; Oct 19th 2008 at 04:57 PM.
simplekin is offline   Reply With Quote
Old Oct 19th 2008, 05:20 PM   #2
Senior Member
 
arbolis's Avatar
 
Join Date: Apr 2008
Posts: 815
The average i calculated in the previous one is 4.4m/s or 15.8km/h
Acceleration has units of $\displaystyle \frac{m}{s^2}$. So if you got an answer with $\displaystyle \frac{m}{s}$ something is wrong.
Anyway, you don't give us what $\displaystyle v_i$ is. Is it $\displaystyle 0\frac{m}{s}$?
I think it would be nice if you could write down the whole problem...
__________________
Isaac
If the problem is too hard just let the Universe solve it.
arbolis is offline   Reply With Quote
Old Oct 19th 2008, 06:08 PM   #3
Junior Member
 
Join Date: Oct 2008
Posts: 2
alright so here is question #1

Try to imagine cars starting up from a stop light. If you were to examine catrs as they start up, you may find that they seem to accelerate constantly for an average 20m in an average time of 3.0 s. Using the formula d=Vi(t)+ (1/2)at^2


question number 2 is this

Using the formula Vf=Vi+at, calculate the velocity of the cars at the end of their initial average acceleration phase. Assume the acceleration is the average one you calculated above. Answer in m/s and km/h.
simplekin is offline   Reply With Quote
Old Oct 19th 2008, 07:13 PM   #4
Senior Member
 
arbolis's Avatar
 
Join Date: Apr 2008
Posts: 815
Ah ok! It was important because we know that $\displaystyle v_0=0$ and even more important : we know that the initial average acceleration phase lasts 3 seconds.
They say
Using the formula Vf=Vi+at, calculate the velocity of the cars at the end of their initial average acceleration phase.
but I'd like to precise a bit more the formula into this one : $\displaystyle v_{final}=v_{initial}+a\cdot t_{final}=a \cdot (3s)=4.44\frac{m}{s^2}\cdot 3s=13.33\frac{m}{s}$ which is the answer.
In fact the problem just asked you to plug values into the given formulas.
__________________
Isaac
If the problem is too hard just let the Universe solve it.
arbolis is offline   Reply With Quote
Reply

  Physics Help Forum > High School and Pre-University Physics Help > Kinematics and Dynamics

Tags
acc, average, calculating, end, initial, phase



Thread Tools
Display Modes


Similar Physics Forum Discussions
Thread Thread Starter Forum Replies Last Post
Initial Velocity randomuser88 Kinematics and Dynamics 5 Jul 23rd 2013 04:58 AM
Finding initial velocity njuice8 Kinematics and Dynamics 0 Jan 21st 2013 08:07 PM
Combining equations of state & calculating phase equilibria from them Robot_Maker20 Advanced Thermodynamics 0 Oct 1st 2010 12:48 PM
initial phase JoanF Kinematics and Dynamics 2 Dec 27th 2009 07:48 AM
Finding Initial Velocity pro222 Kinematics and Dynamics 5 Nov 7th 2009 10:51 PM


Facebook Twitter Google+ RSS Feed