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Homework Help: Newton's law help

  1. Feb 26, 2005 #1
    Hey, i been trying to ask all my friends and trying to read the book over and over. Im having problems with physics, its really hard! I have some questions that im stuck at. I got the basics that F=ma but can someone help me get which equations to use for these questions? Thank you, i have the answers to the questions but i would like to know how to do them thank you again

    a 0.140 kg baseball travels at 35 m/s that strikes the catchers mitt that brings the ball to a stop. It recoils backward at 11.0cm. What is the average force applied by the ball on the glove. I used the basic law and found force of the baseball is 4.9N now where do i input the 11cm?

    a race car can finish a 402 track in 6.40seconds from rest, how many g's does the driev feel? if combined with mass of the driver and race car is 485kg what horizontal force must the road exert on the tires. Im really stuck on the how many g's does he feel and what force is exert on the tires.

    i dont need the answers, just need help on how do i go about analyizing which equations to use for questions. THANK YOU!
  2. jcsd
  3. Feb 26, 2005 #2
    For the first question: remember that f=ma. You tried to find a force by multiplying .14kg by 35m/s, which is mass times velocity, not mass times acceleration.

    To do f=ma you need to know the mass and the acceleration the ball undergoes. You already know the mass because it's explicity given as .14kg. The acceleration is the tricky part. The ball is traveling toward the mitt at 35 m/s and then, over the course of 11cm (.11m) it is brought to 0 m/s. So what kinematic equation do you know that will give you the acceleration if you know 1) initial velocity, 2) final velocity, and 3) distance moved ?
  4. Feb 26, 2005 #3
    a=v(initial)-v(final) / distance?
  5. Feb 26, 2005 #4
    I'd use [tex] v_{f}^2 = v_{0}^2 + 2ad[/tex]
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