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Math Help - physics homework

  1. #1
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    Sep 2008
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    physics homework

    PLEEZ HELP!!!!! these are due at 8. i dont need an explanation of the problem unless u want to but thanks if you help

    #4 PART 1

    Two cars travel in the same direction along a
    straight highway, one at a constant speed of
    55 mi
    /h and the other at 66 mi/h.
    Assuming they start at the same point, how
    much sooner does the faster car arrive at a
    destination 10 mi away? Answer in units of
    min.

    #4 PART 2

    How far must the faster car travel before it
    has a 13 min lead on the slower car? Answer
    in units of mi.

    #6

    A tennis ball with a speed of 8 m
    /s is thrown
    perpendicularly at a wall. After striking the
    wall, the ball rebounds in the opposite direc-
    tion with a speed of 7 m
    /s.
    If the ball is in contact with the wall for
    0
    .012 s, what is the average acceleration of
    the ball while it is in contact with the wall?
    Answer in units of m
    /s2.

    #7

    A subway train starting from rest leaves a
    station with a constant acceleration. At the
    end of 9
    .27 s, it is moving at 22.6188 m/s.
    What is the trainís displacement in the first
    6
    .29433 s of motion? Answer in units of m.


    #8

    Highway safety engineers build soft barriers
    so that cars hitting them will slow down at a
    safe rate. A person wearing a safety belt can
    withstand an acceleration of 300 m
    /s2.
    How thick should barriers be to safely stop
    a car that hits the barriers at 89
    .4 km/h?
    Answer in units of m.


    #9

    Two particles are at the same point at the
    same time, moving in the same direction. Par-
    ticle A has an initial velocity of 7
    .9 m/s and
    an acceleration of 2
    .8 m/s2. Particle B has an
    initial velocity of 2
    .9 m/s and an acceleration
    of 5
    .2 m/s2.
    At what time will B pass A? Answer in

    units of s.
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  2. #2
    Grand Panjandrum
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    Quote Originally Posted by jbrockoli92 View Post
    PLEEZ HELP!!!!! these are due at 8. i dont need an explanation of the problem unless u want to but thanks if you help

    #4 PART 1

    Two cars travel in the same direction along a
    straight highway, one at a constant speed of
    55 mi
    /h and the other at 66 mi/[FONT=CMR10]h.
    Assuming they start at the same point, how
    much sooner does the faster car arrive at a
    destination 10 mi away? Answer in units of
    min.
    Well to travel 10 miles at 66 mph takes 10/66 hours or (10/66) \times 60 minutes.

    The other car takes (10/55) \times 60 minutes.

    Therefor the faster car arrives (10/55) \times 60- (10/66) \times 60 minutes before the slower.


    RonL
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  3. #3
    Grand Panjandrum
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    Quote Originally Posted by jbrockoli92 View Post
    #4 PART 2
    How far must the faster car travel before it
    has a 13 min lead on the slower car? Answer
    in units of mi.
    Generalising from the first part, the faster car arrives at a point x miles from the start point:

    t=(x/55) \times 60 - (x/66) \times 60

    minutes before the slower.

    Now put t=13 and solve for x.

    RonL
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  4. #4
    Grand Panjandrum
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    Quote Originally Posted by jbrockoli92 View Post
    #6
    A tennis ball with a speed of 8 m/s is thrown
    perpendicularly at a wall. After striking the
    wall, the ball rebounds in the opposite direc-
    tion with a speed of 7 m/s.
    If the ball is in contact with the wall for 0.012 s, what is the average acceleration of
    the ball while it is in contact with the wall?
    Answer in units of m/s^2
    Average acceleration = (change in velocity)/time

    RonL
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