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Homework Help: Questions about speed

  1. Sep 16, 2007 #1
    I want to know your opinions on these few questions concerning speed.

    Q1. Man 1 is standing in the back of a pickup truck which is moving at 30 mph. Man 2 is on the side of the road and will use a speed gun to measure how fast a ball is thrown by Man 1. Man 1 throws the ball 30 mph while the truck is moving. So. If the truck is moving 30 mph and Man 1 throws the ball at 30 mph in the direction the truck is moving, how fast will it show up on the speed gun if the speed gun shows the max speed at which the ball is traveling once it leaves Man 1s hand?

    Q2. 2 rockets are traveling through outer space and both are at the traveling exact same speed. Rocket B has twice as much fuel as Rocket A. If there are no gravitational forces acting on or against the rockets such as planets, stars, black holes, asteriods, or the rockets themselves, will Rocket B go faster than Rocket A? And the second question is will Rocket A slow down?
    Last edited: Sep 16, 2007
  2. jcsd
  3. Sep 16, 2007 #2
    Q1 depends entirely on which direction man 1 throws the ball in relation to the motion of the truck.

    Q2. Ok, so you say there is no gravity to account for. We're in space, so I don't see air resistance or friction coming into play. I'm at a loss -- why are they at a max speed? What is there to slow them down at all?

    If B still has fuel left, it can use it and it will accelerate to a higher velocity. Once fuel is out, if there is no force acting on them, the rockets will simply continue at their current velocity. This is a simple application of Newton's 1st law (and the extra fuel part being his second law).
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