Calculating Stopping Time of Car at 77 km/h

[swimstar]

A driver in a car traveling at a speed of 77 km/h sees a cat 107 m away on the road. How long will it take for the car to accelerate uniformly to stop in exactly 103m? Answer in units of s.


I really have no idea where to begin with this problem.

 

[Redbelly98]

Any problem dealing with uniform acceleration starts with the equations for uniformly accelerated motion. Surely these are in your class notes or textbook.

Also, writing out the known quantities (v_initial=___, etc.) would help with this and most other physics problems.

 

[swimstar]

I know that I need to convert 77 km/h to 21. 38888889 m/s which is the initial Velocity.

I was thinking of finding T with the equation d=V(initial)*T. So i could therefore put it in the question in: d=V(initial)*T + 1/2at^2 and solve for a.
However, I am unsure if I use 103m or 107 m in the equations.

Am I doing this correct?

 

[Bartek]

However, I am unsure if I use 103m or 107 m in the equations.

Hint: cat is negligible . This is just a trap. To confuse you what distance to use. And make problem more dramatic.

regards

 

[Redbelly98]

I know that I need to convert 77 km/h to 21. 38888889 m/s which is the initial Velocity.

I was thinking of finding T with the equation d=V(initial)*T.

That is almost the right equation, except that you need v_average, not v_initial. For v_average you may take the average of the initial and final velocities.

So i could therefore put it in the question in: d=V(initial)*T + 1/2at^2 and solve for a.

You could do that, but look again at what the question is asking you to find. (It is not asking for the acceleration.)

However, I am unsure if I use 103m or 107 m in the equations.

The question asks how long it takes for the car to stop in 103 m.