February 13th, 2010, 09:10 PM  #1 
Member Joined: Nov 2009 Posts: 49 Thanks: 0  Variations...
The distance, d m, in which a train can be stopped by its brakes varies partly as the speed, v km/h, and partly as the square of the speed. When running at 10 km/h the train can be stopped in 45 m, and at 20 km/h in 140 m. Find the formula for d in terms of v.

February 14th, 2010, 12:05 AM  #2 
Senior Member Joined: Feb 2009 From: Adelaide, Australia Posts: 1,519 Thanks: 3  Re: Variations...
What it means is that the distance function for a given speed, d(v), is something of the form av²+bv, and you have to find constants a and b. d(10)=45, so 100a+10b = 45 d(20)=140, so 400a+20b = 140 Solve the two simultaneous equations to get a and b. 

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