# SJSU PHYS 2A - Momentum and Collisions (57 pages)

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## Momentum and Collisions

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- Pages:
- 57
- School:
- San Jose State University
- Course:
- Phys 2a - Fundamentals of Physics

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Chapter 6 Momentum and Collisions Introduction Last Chapter W F d E no external nc force means conservation of energy F ma m v t mv t no external force means mv is conserved What is mv Momentum r The linear momentum p of an object ofr mass m moving with a velocity v is defined as the product of rthe mass and the velocity r p mv SI Units are kg m s Vector quantity the direction of the momentum is the same as the velocity s More About Momentum Momentum components px m vx and py m vy Applies to two dimensional motion Momentum is related to kinetic energy p2 KE 2m Impulse In order to change the momentum of an object a force must be applied The time rate of change of momentum of an object is equal to the net force acting on it r p m v f v i r Fnet t t Gives an alternative statement of Newton s second law Impulse cont When a single constant force acts on the object there is an impulse delivered to the object r r I F t r I is defined as the impulse Vector quantity the direction is the same as the direction of the force Impulse Momentum Theorem The theorem states that the impulse acting on the object is equal to the change in momentum of rther object r r r I F t p mv f mv i If the force is not constant use the average force applied Average Force in Impulse The average force can be thought of as the constant force that would give the same impulse to the object in the time interval as the actual time varying force gives in the interval Average Force cont The impulse imparted by a force during the time interval t is equal to the area under the force time graph from the beginning to the end of the time interval Or the impulse is equal to the average force rmultiplied r by the time interval Fav t p Example Impulse Examples Example racquet tension Racquetball goes over 190 mph and tennis goes over 160 mph How tight should you string your racquet to get to that speed Tighter better Kung Fu punch Keep the fist out Impulse Applied to Auto Collisions The most important factor is the

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