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Linear Momentum


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Linear Momentum

  1. 1. Linear Momentum<br />
  2. 2. Momentum<br />Momentum – defined as “mass in motion”<br />Think of 3 objects<br />Car rolling fast down the street<br />Car gently rolling down a driveway<br />A person running along the road<br />Which is hardest to stop?<br />Momentum is the product of mass and velocity<br /><br />Momentum is a vector quanitity measured in <br />
  3. 3. Impulse<br />Throw an egg, build a device to catch it<br />Two ways to stop it<br />Large Force / small time<br />Small Force / large time<br />Impulse is the product of the force applied and the time it is applied for.<br />A car of 1500kg traveling at 45m/s hits a brick wall and comes to a stop in .001m. What is the acceleration of the driver. What is the Force applied to the driver?<br />
  4. 4. Remember F=ma, and <br />Therefore<br />Multiply t and we have <br />This gives us<br />or <br /> Since momentum is the product of mass and velocity<br />Momentum – Impulse Therom<br />
  5. 5. Collisions<br />Two types Elastic and Inelastic<br />Elastic<br />Momentum is conserved<br />TME is conserved<br />Generally involves rebound<br />Inelastic<br />Momentum is conserved<br />TME is not conserved<br />Generally involves two objects sticking together<br />
  6. 6. Explosions<br />When two objects are together and then separate it is called an explosion in physics.<br />This applies to real explosions as well as other situations<br />An explosion still conserves all momentum. Because initially the system has zero momentum, the resultant momentum must sum to zero.<br />Kent Swimm, who is taking Physics for the third year in a row (and not because he likes it), has rowed his boat within three feet of the dock. Kent decides to jump onto the dock and turn around and dock his boat. Explain to Kent why this docking strategy is not a good strategy.<br />
  7. 7. A rifle of mass 3.6kg fires a bullet with a mass of 20g at a velocity of 667.23m/s. How far does the rifle recoil?<br />0.371m / Explosion<br />An open cart on a level surface is rolling without frictional loss through a vertical downpour of rain, as shown above. As the cart rolls, an appreciable amount of rainwater accumulates in the cart. The speed of the cart will<br />(A) increase because of conservation of momentum <br />(B) increase because of conservation of mechanical energy <br />(C) decrease because of conservation of momentum <br />(D) decrease because of conservation of mechanical energy <br />(E) remain the same because the raindrops are falling perpendicular to the direction of the cart&apos;s motion<br />
  8. 8. A 70 kg woman and her 35 kg son are standing at rest on an ice rink, as shown above. They push against each other for a time of 0.60 s, causing them to glide apart. The speed of the woman immediately after they separate is 0.55 m/s. Assume that during the push, friction is negligible compared with the forces the people exert on each other.<br />Calculate the initial speed of the son after the push.<br />Calculate the magnitude of the average force exerted on the son by the mother during the push.<br />How do the magnitude and direction of the average force exerted on the mother by the son during the push compare with those of the average force exerted on the son by the mother? Justify your answer.<br />After the initial push, the friction that the ice exerts cannot be considered negligible, and the mother comes to rest after moving a distance of 7.0 m across the ice. If their coefficients of friction are the same, how far does the son move after the push?<br />