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Chapter 6
Momentum and Collisions1. Momentum and Impulse2. Conservation of Momentum3. 1D Collisions4. 2D Collisions
Example – Momentum and Impulse 1. A 50-g golf ball is struck with
a club as shown. The force on the ball varies from zero when contact is made up to some maximum value (when the ball is deformed) and then back to zero when the ball leaves the club. The force-time graph is also shown. Assume the ball leaves the club face with a velocity of +44m/s
1. Estimate the size and direction of the impulse due to the collision.
2. Estimate the duration of the collision and the average force on the ball.
Injury in Car CollisionData:Survival data for head on
collision: Force for bone fracture 90KN, Pressure 1.9x105N/m2 at 60 mi/h resulting in acceleration of 50g’s for 70 ms for an area of 0.7-0.9 m2
Case Data Mp = 75-kg, Vi =60 mi/h (27m/s), tr=0.010 s, Achest+head=0.5 m2
Find F, a, P
Air Bags and Seat Belts The air bag increases
the time of the collision
It will also absorb some of the energy from the body
It will spread out the area of contact
decreases the pressure
helps prevent penetration wounds
Conservation of Momentum What is this conservation law? What do we mean by a system? What do we mean by an isolated
system? Is contact necessary? Another way to say the same thing
Example – Inelastic Collision1. A bullet of mass m with a speed v into a
wooden block of mass M. Find an expression that gives the initial velocity of the bullet in terms of masses, acceleration due to gravity g and the height h thru which the pendulum is raised.
Example – Elastic Collision1. A bullet of mass m and
speed v passes completely through a pendulum bob of mass M. The bullet emerges with a speed v/2. The pendulum bob is suspended by a stiff rod of length l and negligible mass. What is the minimum value of v such that the pendulum bob will barely swing through a complete vertical circle? (Find the expression in terms M, m g and l).
Example – Glancing Collision1. A 1500kg car traveling
east with a speed of 25 m/s collides at an intersection with a 2500kg van traveling north at a speed of 20 m/s as shown. Find the direction and magnitude of the velocity of the wreckage after the collision, assuming that the vehicles undergo a perfectly inelastic collision (that is, they stick together) and assuming that friction between the vehicles and the road can be neglected.