A motorist travels at a constant speed of 38.0 m/s through a school zone, exceeding the posted speed limit. A policeman waits 7.0 s before giving chase at an acceleration of 3.5 m/s^2.
Find the time required to catch the car from the instant the car passes the policeman.
My work:
x(car)=X(b)+V(x/car) -------- t=266m +(38.0m/s)t
x(trooper)=(1/2)(3.5 m/s^2)t^2
x(trooper)=x(car)------(1/2)(3.5 m/s^2)t^2 = 266 m + (38.0m/s)t
1.75t^2 - 38.0t - 266
When I factor and take the positive I get: 27.3
But when I put this into the answer box it tells me its wrong do I need to add 7 sec on the end? Please help me?
Thanks
Find the time required to catch the car from the instant the car passes the policeman.
My work:
x(car)=X(b)+V(x/car) -------- t=266m +(38.0m/s)t
x(trooper)=(1/2)(3.5 m/s^2)t^2
x(trooper)=x(car)------(1/2)(3.5 m/s^2)t^2 = 266 m + (38.0m/s)t
1.75t^2 - 38.0t - 266
When I factor and take the positive I get: 27.3
But when I put this into the answer box it tells me its wrong do I need to add 7 sec on the end? Please help me?
Thanks
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Correct. In your equation at t=0, the car is 266m ahead. You've calculated the catch from that point in time.
But the question asks you how long it takes to catch up from the time the car passes the policeman.
But the question asks you how long it takes to catch up from the time the car passes the policeman.
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that's what I get, too
Are significant figures the problem?
maybe it wants 27 m/s not 27.3 m/s
Are significant figures the problem?
maybe it wants 27 m/s not 27.3 m/s
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Yes you have to add the 7 seconds.