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A car blows past a trap going 162 km/h. A police car starts to move 5 seconds after the speeding car passes it, accelerating at 6 m/s^2. How long will it take the police car to catch the speeder?

 

Please provide explanations and full solutions!

 

Thanks, very much!

 Nov 23, 2016

Best Answer 

 #6
avatar+36915 
+5

You are correct....that was in my correction.....but you may have posted before I corected it!  Good call!

 Nov 23, 2016
 #1
avatar+72 
+5

If this helps, the answer is 30.4 seconds. However, I always get different solutions. 

 Nov 23, 2016
 #2
avatar+36915 
+5

MT.....does the car keep accelarating until it catches the speedster in your answer?

 Nov 23, 2016
 #3
avatar+72 
+5

Acceleration is constant.

MapleTheory  Nov 23, 2016
 #4
avatar+36915 
+5

 

CORRECTION:      wrong units    corrected below and added distance for 5 seconds

 

 

Speedster displacement= 162 k/hr  x t      Which equals   162 x 1000/=3600 m/s = 45 m/s       45 x t    + (45 x 5) = displacement

 

Police car  x= displacement = x0 + vo t + 1/2 at^2     (x0=0  vo t =0)  and it has to equal     45 x t + 225

 

so

45t +225 = 1/2 at^2

90t +450 = at^2     and a=6

6t^2 - 90t-450=0

t^2 -15t-75=0

Quad formula    15+-sqrt(225+300)  / 2  =     18.95 seconds

 

 

Hope i did that correctly!                                       

 Nov 23, 2016
edited by ElectricPavlov  Nov 23, 2016
edited by ElectricPavlov  Nov 23, 2016
 #5
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EP: I don't know much about physics, but shouldn't the 5 seconds' delay by the police officer be taken into account in the sense that the speeder has already travelled: 5 x 45 =225 meters??.

 Nov 23, 2016
 #6
avatar+36915 
+5
Best Answer

You are correct....that was in my correction.....but you may have posted before I corected it!  Good call!

ElectricPavlov  Nov 23, 2016

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