Calculating Time for Side-by-Side Cars: Car Kinematics Homework

  • Thread starter Thread starter Youngstabullz
  • Start date Start date
  • Tags Tags
    Car Kinematics
AI Thread Summary
The discussion revolves around calculating the time it takes for a red car, which accelerates from rest to 34.3 m/s in 8.92 seconds, to catch up with a blue car traveling at a constant speed of 21.5 m/s. The user attempted to set the distances equal using kinematic equations but struggled to find the correct time. A member provided hints on the calculations, emphasizing the need to account for the red car's constant speed after acceleration. Another user cautioned against giving complete answers to encourage problem-solving. Ultimately, the correct time for the two cars to be side-by-side is determined to be approximately 11.95 seconds.
Youngstabullz
Messages
2
Reaction score
0

Homework Statement



A red car is sitting at a stop light at rest. When the light turns green two things happen simultaneously; (1) the red car accelerates to a speed of 34.3 m/s in 8.92 seconds and then maintains that 34.3 m/s speed and (2) a blue car passes by the red car at a constant speed of 21.5 m/s.

Red Car: Vo=0 Vf=34.3 m/s a=3.84 (34.3/8.92)
Blue Car: Vo=21.5 m/s Vf=21.5 m/s

How much time (in seconds) will have elapsed from when the light turned green until the two cars are side-by-side?

52827?db=v4net.gif


Homework Equations



distance = 1/2(Vo + Vf)t
distance = Vot + 1/2at^2


The Attempt at a Solution



I thought I would make them equal to each other, 1/2(Vo +Vf)t=Vot +1/2at^2 And find out what t equals to find out the time however It has yet to work after many attempts. Vo Any help is appreciated.
 
Last edited by a moderator:
Physics news on Phys.org
Welcome to PF!

Youngstabullz said:
A red car is sitting at a stop light at rest. When the light turns green two things happen simultaneously; (1) the red car accelerates to a speed of 34.3 m/s in 8.92 seconds and then maintains that 34.3 m/s speed and (2) a blue car passes by the red car at a constant speed of 21.5 m/s.

Red Car: Vo=0 Vf=34.3 m/s a=3.84 (34.3/8.92)
Blue Car: Vo=21.5 m/s Vf=21.5 m/s

How much time (in seconds) will have elapsed from when the light turned green until the two cars are side-by-side?

I thought I would make them equal to each other, 1/2(Vo +Vf)t=Vot +1/2at^2 And find out what t equals to find out the time however It has yet to work after many attempts.

Hi Youngstabullz! Welcome to PF! :smile:

Show us your calculations, and then we can see where you've gone wrong. :smile:

(you have allowed for the period of constant speed of 34.3, haven't you?)
 
x(blue)=21.5*8.92+21.5*t

x(red)=.5*34.3*8.92+34.3*t

and so t=3.03 then the answer is answer=3.03+8.92=11.95 seconds
 
rado5 said:
x(blue)=21.5*8.92+21.5*t

x(red)=.5*34.3*8.92+34.3*t

and so t=3.03 then the answer is answer=3.03+8.92=11.95 seconds

Hi rado5! :smile:

You must stop giving full answers to other people's questions (you've done it before).

You haven't even given Youngstabullz the chance to reply. :frown:

On this forum, we try just to give helpful hints, so that the OP can work the problem out themselves.

Full answers should only be given when all hints have failed.

Please restrain yourself. :smile:

(And your answer was wrong … again! :rolleyes:)
 
Thankfully, I got the answer before you guys had responded to my question. :D
 
Youngstabullz said:
Thankfully, I got the answer before you guys had responded to my question. :D

That's the idea! :smile:
 
Kindly see the attached pdf. My attempt to solve it, is in it. I'm wondering if my solution is right. My idea is this: At any point of time, the ball may be assumed to be at an incline which is at an angle of θ(kindly see both the pics in the pdf file). The value of θ will continuously change and so will the value of friction. I'm not able to figure out, why my solution is wrong, if it is wrong .
TL;DR Summary: I came across this question from a Sri Lankan A-level textbook. Question - An ice cube with a length of 10 cm is immersed in water at 0 °C. An observer observes the ice cube from the water, and it seems to be 7.75 cm long. If the refractive index of water is 4/3, find the height of the ice cube immersed in the water. I could not understand how the apparent height of the ice cube in the water depends on the height of the ice cube immersed in the water. Does anyone have an...
Back
Top