Newton's Laws and Momentum

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  • Created by: Agata
  • Created on: 24-02-16 16:03
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  • Newton's Laws  and Momentum
    • Momentum
      • LINEAR MOMENTUM: The mass of an object multiplied by its velocity. It is a VECTOR. (symbol: p , units kg*m/s).
        • p = mv
        • The reason for using the term linear momentum is that there is another term, angular momentum for objects rotating.
      • Momentum  = force x distance= change in momentum        Ft=mv-mu        Unit: Ns          VECTOR
    • WORKED EXAMPLE      A truck going north along a motorway has a mass of 4000 kg and a velocity of 18 m/s. A car also going north along the motorway, has a mass of 1400 kg and a velocity of 35 m/s .
      • A) Calculate the kinetic energy of each vehicle.  ANSWER: Truck : 1/2 x 4000 x 18 ^2 = 648 000 J.   Car: 1/2 x 1400 x 35^2 = 857500.
        • kinetic energy = 1/2 m v ^"
      • C) Calculate the distance each vehicle takes to stop against retarding force of 7000N         ANSWER Truck: 18^2/( 2 x 1.75 ) = 92.6m       Car: 35^2 /(2 x 5.0) = 122.5m
        • s=v^2/2a
    • Kinetic Energy    K.E= force x distance = change in K.E   Fd=1/2mv^2- 1/2mu^2            Unit: Nm = J     SCALAR
  • B) Calculate the momentum of each vehicle. ANSWER  Truck: 4000 x 18 = 72 000 due north          Car: 1400 x 35 = 49 000 due north.
    • p=mv
    • WORKED EXAMPLE      A truck going north along a motorway has a mass of 4000 kg and a velocity of 18 m/s. A car also going north along the motorway, has a mass of 1400 kg and a velocity of 35 m/s .
      • A) Calculate the kinetic energy of each vehicle.  ANSWER: Truck : 1/2 x 4000 x 18 ^2 = 648 000 J.   Car: 1/2 x 1400 x 35^2 = 857500.
        • kinetic energy = 1/2 m v ^"
      • C) Calculate the distance each vehicle takes to stop against retarding force of 7000N         ANSWER Truck: 18^2/( 2 x 1.75 ) = 92.6m       Car: 35^2 /(2 x 5.0) = 122.5m
        • s=v^2/2a
  • D) Calculate the time each vehicle takes to stop against a retarding force of 7000N. ANSWER       Truck: 18/1.75=10.3s  Car: 35/5=7.0s
    • t=v/a

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