Friday, August 21, 2015

Dynamics | 9702 Physics Summary Notes

  • 4. Dynamics | 9702 Physics Summary Notes



4.1 Newton’s Laws of Motion

·  First law: if a body is at rest it remains at rest or if it is in motion it moves with a uniform velocity until it is acted on by resultant force or torque
·  Second law: the rate of change of momentum of a body is proportional to the resultant force and occurs in the direction of force; F=ma
·  Third law: if a body A exerts a force on a body B, then body B exerts an equal but opposite force on body A, forming an action-reaction pair


4.2 Mass and Weight

Mass
Weight
·  Measured in kilograms
·  Scalar quantity
·  Constant throughout the universe
·  Measured in Newtons
·  Vector quantity
·  Not constant
·  W=mg
·  Mass: is a measure of the amount of matter in a body, & is the property of a body which resists change in motion.
·  Weight: is the force of gravitational attraction (exerted by the Earth) on a body.


4.3 Momentum

· Linear momentum: product of mass and velocity
p = mv
· Force: rate of change of momentum
F = (mv - mu) / t
· Principle of conservation of linear momentum: when bodies in a system interact, total momentum remains constant provided no external force acts on the system.
mAuA + mBuB = mAvA + mBvB


4.4 Elastic Collisions

· Total momentum conserved
· Total kinetic energy is conserved
Example: Two identical spheres collide elastically. Initially, X is moving with speed v and Y is stationary. What happens after the collision? 

X stops and Y moves with speed v
Relative velocity before collision = Relative velocity after collision

uA - uB = vB - vA




4.5 Inelastic Collisions

relative speed of approach > relative speed of separation
o Total momentum is conserved
· Perfectly inelastic collision: only momentum is conserved, and the particles stick together after collision (i.e. move with the same velocity)
· In inelastic collisions, total energy is conserved but Ek may be converted into other forms of energy e.g. heat 





3 comments:

  1. i need help in this question
    Q: A stationary nucleus of mass 220u undergoes radioactive decay to produce a nucleus D of mass 216u and alpha particle of mass 4u
    the initial kinetic energy of the alpha particle is 1*10^-12(one times ten to the power of negative twelve)
    A) (i)state the law of conservation of linear momentum
    (ii) explain why the initial velocities of the nucleus D and the alpha particle must be in opposite directions
    B)(i) show that the initial speed of alpha particle in 1.7*10^7 m/s
    (ii)calculate the initial speed of nucleus D
    c) the range in air of the emitted alpha particle is 4.5 cm
    calculate the average deceleration of the alpha particle as it is stopped by the air

    ReplyDelete
  2. A stationary nucleus of mass 220u undergoes radioactive decay to produce a nucleus D of
    mass 216u and an α-particle of mass 4u

    The initial kinetic energy of the α-particle is 1.0 × 10^–12 J.
    (ii) Explain why the initial velocities of the nucleus D and the α-particle must be in
    opposite directions.
    (b) (i) Show that the initial speed of the α-particle is 1.7 × 10^7 m/s.
    (ii) Calculate the initial speed of nucleus D.
    (c)The range in air of the emitted α-particle is 4.5 cm.
    Calculate the average deceleration of the α-particle as it is stopped by the air.

    ReplyDelete
    Replies
    1. Check solution 1098 at
      http://physics-ref.blogspot.com/2016/02/physics-9702-doubts-help-page-234.html

      Delete

If it's a past exam question, do not include links to the paper. Only the reference.
Comments will only be published after moderation

Currently Viewing: Physics Reference | Dynamics | 9702 Physics Summary Notes