Chapter 6 • General Physics
Momentum and Impulse • Momentum: • Newton’s Second Law: • Impulse:
Example • “The Babe” points to the grandstands behind the pitching mound, infuriating the pitcher. The pitcher then throws a fastball (44.7m/s, 145g) right down the middle. The Babe smacks the pitch and sends the ball right where he pointed at 69.4 m/s (30o above the ball’s original path). The ball was in contact with the bat for 0.71 ms. What average force did “The Babe” apply to the ball?
Average vs. Actual Average Reality
Conservation of Momentum • Works for collisions and explosions • Types of Collisions: • Elastic (bouncy) Both KE and P are conserved • Inelastic (not bouncy) Only P is conserved
Example: Inelastic • mass of the ball = 0.065852 Kg • mass of the bob = 0.241511 Kg • length of bob = 31.32 cm • Big huge assumption (for simplicity): all the mass of the bob is at the bottom where the ball is caught. • What was the launch velocity of the ball?
Example: Elastic Collision • Problem 6.38 • Two disks of equal mass hit and bounce perfectly. The orange disk is initially at rest and is struck by the blue disk which is moving to the right at 5 m/s. After the collision the blue disk moves in a direction that makes an angle of 37.0o to the original direction. Meanwhile, the velocity of the orange disk is perpendicular to that of the blue disk. What is the speed of the disks after the collision?
Example • KITT and Goliath head toward each other at 45 m/s each. KITT has a mass of 400 Kg while Goliath has a mass of 2,000 Kg. Find their velocities after the elastic collision.
Acknowledgments • The Babe: http://www.top20lists.com/2010/06/top-twenty-sportsman-of-all-time.html • Baseball impulse: http://memagazine.asme.org/Articles/2010/April/Our_Favorite_Pastime.cfm • KITT: http://i131.photobucket.com/albums/p314/firebirdta84/22-Goliathmpg_001614436.jpg • Goliath: http://local.aaca.org/junior/starcars/kitt/goliath.jpg • All other pictures came from our Cengage learning (our textbook)