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Homework Help: Equations of Motion

  1. Mar 5, 2014 #1
    The head of a snake can accelerate at 50 m/s2when it strikes. The snake’s head starts from rest and
    accelerates constantly until it strikes a victim that is 0.5 m away.
    a) How fast is the snake’s head moving when it hits the victim?
    b) How long does it take the snake’s head to get to the victim?

    Q 2. A rocket coasting at 20,000 m/s in deep space fires its engines so that it accelerates at 20 m/s2.
    a) How long will it have to keep accelerating to get to a speed of 300,000 m/s?
    b) How far will it travel while it is accelerating?

    Q 3. A world land speed record was set by Mr. John when he rode a rocket-propelled sled at 283.3 m/s. The
    sled was brought to a stop in 1.4s. What acceleration did Mr. John experience?

    Q 4. A high-speed train starts from rest and moves with constant acceleration. As it passes a speed trap, a
    bored police officer uses a radar gun to measure the train’s speed as 30 m/s. At another speed trap, 160 m
    further down the track, another officer measures the train’s speed as 50 m/s.
    a) How quickly was the train accelerating?
    b) How long did it take to travel the 160 m between speed traps?

    Q 5. A boy is inspired by Mr. John’s example to take up rocket sledding. He builds a track so he can get a
    modern rocket sled to go from rest up to 445 m/s. If his track is only 225 m long, how quickly will boy (and
    sled) have to accelerate to reach the target speed by the end of the track?
  2. jcsd
  3. Mar 5, 2014 #2


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    For number one, refer to the definition of acceleration. What is it equal to? Play with the variables to solve for the variable you are seeking (which is the speed in this case). The same applies to the other 4.

    edit: Think of the kinematics equations and how you can apply them to the problems.
  4. Mar 5, 2014 #3
    Thanks, i need the answer keys of this questions!
  5. Mar 5, 2014 #4


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    Sorry, but here we don't give out answers. You're expected to find the answer yourself with help from us if it is (and apparently it is) required. What don't you understand in the problems? Can you write the 5 kinematics equations (not the definitions of position, velocity, and acceleration)? If not, then you should check the textbook you have or review your notes.
  6. Mar 5, 2014 #5


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    The best way to practice is to write down the 4 equations on a paper and write the variables given by the question.Then search for the relevant equation which fits for all the variables(You may have to find some variables yourself (eg:Speed when distance and time is given))
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