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1) A car traveling at 22m/s decelerates at a constant 1.5m/s^2. Calculate the time it takes to stop.
I first calculated the distance which is 160 m. Then I used the formula d=vit+1/2at^2. I got a quadratic -0.75t^2+22t-160. I got 13 or 16 as my time, but the answer says 15. Would it be correct to take the average of those times?

2) A stone is dropped from the roof of a high building. A second stone is dropped 1s later. How far apart are the stones when the second one has reached a speed of 23.0m/s?
I set this problem up by writing the given for stone 1 and stone 2.
Some equations I got were d(s1)= 4.905t^2 and ts2=ts1+1

I don't know how to do the problem.

  • Physics -

    1. No, not the average.


    Your method rounded distance to 160m. If you had not rounded, you would have gotten 15 seconds....

    2.find the time of the first to get to that speed.
    vf=gt solve for t, and the distance fell.
    Now, subtract one from that t, and find out how far the second fell.

    Subtract the distances.

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