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Bebo_momo · Jul 31, 2014, 05:30 AM

On a foggy day, two drivers spot in front of each other when 80 meter apart. They were traveling at 70kmph and 60kmph. Both apply brakes simultaneously which retard the cars at the rate of 5 [m/s²]. Which of the following statements is correct?
a) The collision will be averted
b) The collision will take place
c) They will cross each other
d) They will just collide.

ebaines · Jul 31, 2014, 06:09 AM

Find the distance it takes each to stop. Given initial velocity and acceleration, do you know which equation of motion involves distance?

Bebo_momo · Jul 31, 2014, 08:17 AM

Originally Posted by ebaines

Find the distance it takes each to stop. Given initial velocity and acceleration, do you know which equation of motion involves distance?

Yes Ebaines..
s= ut + 1/2 at²
and, v²- u²= 2as
s= distance

ebaines · Jul 31, 2014, 08:29 AM

Originally Posted by Bebo_momo

Yes Ebaines..
and, v²- u²= 2as

Good - so what do you get as values for s for the two cars?

Bebo_momo · Jul 31, 2014, 09:44 AM

Actually I don't know whether the given velocities are 'v' or 'u'??

Bebo_momo · Jul 31, 2014, 09:52 AM

37.6 m for first one and 27.5 m for the second one?? Is it so??
:( See, I am very weak in Kinematics. If I am wrong then don't make a fun of me...

ebaines · Jul 31, 2014, 11:35 AM

Close - I get 37.8m and 27.8m.

In the equation v^2-u^2 = 2as, v is the starting velocity and u= ending velocity of an object So in this case v is 70 KPH for one car and 60 KPH for the other, and u is 0 for both. I prefer writing the equation as:

$v_i^2 - v_f^2 = 2ad$

where $v_i$ is initial velocity and $v_f$ is final velocity, but you should use whatever terms your book uses.

Bebo_momo · Aug 2, 2014, 10:23 AM

Thanks Ebaines! :)