1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Help with simple HW problems please

  1. Feb 2, 2010 #1
    Help with simple HW problems please!!

    1. Two cars drive off a cliff. The road was completely horizontal until it ended (launching the cars off the cliff with an initail velocity in the horizontal direction). Car A was driving at 80 m/s, and Car B was driving at 20 m/s when they left the cliff. Assume you can ignore wind resistance and friction in this problem.

    a) Which car (if any) hits the water at the bottom of the cliff first? Why?

    b) Which car (if any) travels further in the air before it hits the water? Why?

    2. If the cliff is 17 m high, calculate how long each car is in the air.

    3. A bullet is shot out of a gun at a 45 degree angle above horizontal. We will call the height of the gun zero height. When the bullet reaches its highest point in its trajectory, which of the following must be true?

    The acceleration of the bullet is zero.
    The velocity of the bullet is zero.
    The height of the bullet is zero
    All of the above
    None of the above

    4. Explain your answer to the multiple choice question above.



    Relevant Equations x=x(0) + v(0x)t
    y=y(0) + v(0y)t - (.5)g(t^2)



    The attempt at a solution

    1. a) They will both hit the water at the same time, because they both fall at the same rate of acceleration (ay=-9.8 m/s^2).

    b) Car A will have a higher range of travel, because it starts with a higher horizontal velocity.

    2. 0=17-(.50)(9.80)t^2
    -17=(-4.9)t^2
    3.5=t^2
    t=1.9 seconds

    This applies to both cars, because both leave the cliff with the same rate of acceleration in the y axis (ay=-9.80), and the same starting velocity in the y axis (ay=0).

    3. None of the Above

    4. The acceleration of the bullet is 0 in the x-axis, but it remains -9.80 in the y axis.

    The velocity of the bullet is zero in the y-axis when it is at its highest point, but its velocity in the x-axis is constant.

    The height of the bullet is not zero if the height of the gun is considered zero height.
     
  2. jcsd
  3. Feb 2, 2010 #2

    mgb_phys

    User Avatar
    Science Advisor
    Homework Helper

    Re: Help with simple HW problems please!!

    Correct
     
  4. Feb 2, 2010 #3

    Delphi51

    User Avatar
    Homework Helper

    Re: Help with simple HW problems please!!

    All answers look good to me.
     
  5. Feb 2, 2010 #4
    Re: Help with simple HW problems please!!

    Thanks!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Help with simple HW problems please
Loading...