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

Challenging Question

  • #1
243
0
A car is observed to cross an intersection in 4s. If the intersection is 40 meters wide, and the car accelerated at 3.3m/s^2, calculate its speed when half-way across the intersection.

I have been having a tought time with this problem because I'm not sure what the initial speed is. Also I don't know what the time would be at half. Its confusing, please help
 

Answers and Replies

  • #2
arildno
Science Advisor
Homework Helper
Gold Member
Dearly Missed
9,970
131
1. You know the time when it has travelled 40meters, and the constant acceleration during that period.
Use this info to determine the initial velocity, from the equation giving you the distance travelled as a function of t.
2. Determine the value of "t" when the car has travelled 20 meters (from the same equation for the position).
Insert that value of "t" into your expression for the velocity at time "t".
 
  • #3
243
0
what is the equation?
 
  • #4
243
0
someone still help explain more i'm still not getting it
 
  • #5
Pyrrhus
Homework Helper
2,178
1
Use arildno reasoning with the kinematic equations for uniform acceleration

[tex] info: [/tex]
[tex] x_{o} = 0 m [/tex]
[tex] x = 40 m [/tex]
[tex] a = 3.3 m/s^2 [/tex]
[tex] t = 4s [/tex]


Using this equation you can get the initial speed

[tex] x - x_{o} = v_{o}t + \frac{1}{2}at^2 [/tex]

Now using the same equation, you can get the time t, with a displacement of 20 m and same acceleration

[tex] x - x_{o} = v_{o}t + \frac{1}{2}at^2 [/tex]

Now using this equation, you can plug in the time t, and find the speed at that time (at 20 m)

[tex] v = v_{o} + at [/tex]

arildno answer couldn't be any more clear.
 

Related Threads for: Challenging Question

  • Last Post
Replies
7
Views
2K
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
8
Views
1K
  • Last Post
Replies
3
Views
1K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
8
Views
3K
  • Last Post
Replies
5
Views
2K
Top