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Math Help - velocity/acceleration

  1. #1
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    velocity/acceleration

    A dragster races down a 400 m strip in 8 seconds. Its distance, in metres, from the starting line after t seconds is s(t)=6t^2+2t

    a) find the dragster's velocity and acceleration as it cross the finish line.

    b) how fast was it moving 60 m down the strip?

    I need help with part b.. I thought that i would use the acceleration formula i made up in part a but it did not work out since the a(t) formula in part a is a constant number > 12

    Help with part b. thanks
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
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    Quote Originally Posted by skeske1234 View Post
    A dragster races down a 400 m strip in 8 seconds. Its distance, in metres, from the starting line after t seconds is s(t)=6t^2+2t

    a) find the dragster's velocity and acceleration as it cross the finish line.

    b) how fast was it moving 60 m down the strip?

    I need help with part b.. I thought that i would use the acceleration formula i made up in part a but it did not work out since the a(t) formula in part a is a constant number > 12

    Help with part b. thanks
    how did you do (a)?

    For (b), set s(t) = 60 and solve for t. Then plug that t-value into the velocity equation to find its velocity at that time (why would you use acceleration??)
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  3. #3
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    All you need to do is set s(t)=6t^2+2t=60m and use the quadratic formula to solve for t. Take the solution and plug it into s'(t)=12t to obtain the velocity at 60m. If you don't remember the formula to solve 6t^2+2t-60=0 for t, just look it up on wikipedia. Or just factor the equation. I'm bad at factoring, so I always just use the quadratic formula.
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