• Support PF! Buy your school textbooks, materials and every day products Here!

Finding car speed

  • Thread starter vaironl
  • Start date
  • #1
34
0

Homework Statement


A race car starting from rest accelerates uniformly at a rate of [itex]4.90m/s^{2}[/itex] . What is the car's speed after it has traveled 200m?

Homework Equations



Δv = [itex]\frac{Change in position}{change in time}[/itex]

The Attempt at a Solution


v=[itex]\sqrt{980m^2/s^2}[/itex]

=31.3m/s
 

Answers and Replies

  • #2
SammyS
Staff Emeritus
Science Advisor
Homework Helper
Gold Member
11,256
974

Homework Statement


A race car starting from rest accelerates uniformly at a rate of [itex]4.90m/s^{2}[/itex] . What is the car's speed after it has traveled 200m?

Homework Equations



Δv = [itex]\frac{Change in position}{change in time}[/itex]

The Attempt at a Solution


v=[itex]\sqrt{980m^2/s^2}[/itex]

=31.3m/s
Show your work so that we can help you see where your error is.

How did you get [itex]v=\sqrt{980m^2/s^2}\,?[/itex]
 
  • #3
gneill
Mentor
20,792
2,770
What kinematic formula are you using? It looks like you've missed out a constant.
 
  • #4
34
0
Show your work so that we can help you see where your error is.

How did you get [itex]v=\sqrt{980m^2/s^2}\,?[/itex]
What kinematic formula are you using? It looks like you've missed out a constant.
Well I'm required to find the speed after 200 meters, but I was never given any time.

So I assume... Which is not a good thing to do, multiplying the acceleration * the distanced travel would give me the speed.

But I really can't remember the actual equation.
 
  • #5
gneill
Mentor
20,792
2,770
Well I'm required to find the speed after 200 meters, but I was never given any time.

So I assume... Which is not a good thing to do, multiplying the acceleration * the distanced travel would give me the speed.

But I really can't remember the actual equation.
If you can't remember you should check your notes or text book! Your formula is close to being a valid kinematic expression,... but it's missing a constant. Do you have a list of the common kinematic expressions?
 
  • #6
34
0
If you can't remember you should check your notes or text book! Your formula is close to being a valid kinematic expression,... but it's missing a constant. Do you have a list of the common kinematic expressions?
I have the text book, and I did have an example sheet but my friend borrowed to check her work. I found this expression which seems to satisfy my problem, v2 = vo2 + 2a(X - Xo)

Therefore V2= 0m/s + 2(4.90m/s^2)(200m)

v2= 9.8m/s^2(200m)
v2= 1960m^2/s^2
v=[itex]\sqrt{1960m^2/s^2}[/itex]
v= 44.3m/s
 
  • #7
gneill
Mentor
20,792
2,770
I have the text book, and I did have an example sheet but my friend borrowed to check her work. I found this expression which seems to satisfy my problem, v2 = vo2 + 2a(X - Xo)

Therefore V2= 0m/s + 2(4.90m/s^2)(200m)

v2= 9.8m/s^2(200m)
v2= 1960m^2/s^2
v=[itex]\sqrt{1960m^2/s^2}[/itex]
v= 44.3m/s
That looks better :smile:
 

Related Threads on Finding car speed

  • Last Post
Replies
10
Views
5K
  • Last Post
Replies
1
Views
454
  • Last Post
Replies
3
Views
4K
  • Last Post
Replies
3
Views
7K
  • Last Post
Replies
3
Views
1K
Replies
2
Views
4K
Replies
6
Views
3K
  • Last Post
Replies
3
Views
2K
  • Last Post
Replies
11
Views
2K
Replies
5
Views
8K
Top