A car 4m long came up behind a semi-trailer 20m long travelling at a steady 72km/h. After travelling behind the semi-trailer for some time, the driver of the car decided to overtake. If the car pulled out from behind the semi-trailer with the front of the car 10m behind the rear of the trailer and accelerated at 3.5m/s/s until the rear of the car was 10m in front of the truck, how far would the car travel and how long would it take?

I used 44m as displacement, and got velocity from that, which I then used to get time. But my answers are wrong. Any ideas?

Question

A car 4m long came up behind a semi-trailer 20m long travelling at a steady 72km/h. After travelling behind the semi-trailer for some time, the driver of the car decided to overtake. If the car pulled out from behind the semi-trailer with the front of the car 10m behind the rear of the trailer and accelerated at 3.5m/s/s until the rear of the car was 10m in front of the truck, how far would the car travel and how long would it take?

I used 44m as displacement, and got velocity from that, which I then used to get time. But my answers are wrong. Any ideas?

anonymous · Answer

how did you get 44m as a displacement?

anonymous · Answer

The whole overtaking process. 4 + 10 + 20 + 10

anonymous · Answer

ok then 
 I think you are looking for
s=v0t+(at^2)/2


where
v0=initial velocity a=acceleration t=time elapsed and s=distance traveled

anonymous · Answer

I don't have any value for t though.

anonymous · Answer

you are solving for t, the initial velocity is zero as well. 
The really questions is how long does it take to travel 44m is accelerating at 3.5 m/s
Both the car and truck are moving at the same speed, at the start, the 72km/h doesn't matter

anonymous · Answer

Solving that equation for t has never really worked for me. Would t = v-u/a work?

anonymous · Answer

44=(3.5t^2)/2
88=(3.5t^2)
88/3.5 is about 25, so the answer is about 5 sec

anonymous · Answer

Acceleration is a "compounding" effect, so the speed, curves and there the power of 2
if that make any sense to you

anonymous · Answer

You're right. The correct answer is 5. But I'm still a little confused, what formula was that using? And that kind of makes sense, but I'm not sure how that fits into the equation..

anonymous · Answer

?

anonymous · Answer

try the formula S=ut+1/2a(t)square

anonymous · Answer

Been there, done that.

anonymous · Answer

|dw:1328950368721:dw|
suppose car overtakes in time t, then total distance covered by DRIVER OF TRAILER=20t
+we add the legth of trailer as only driver and front are moving
next cars driver moves 10m+10m+20t+20m+4m(its own length)
then u would have s=1/2at^2 formula to use
the thiung is that consider the drivers of car and truck next consider the rest of the portion of vehicles