Unit 3 Lesson 6 Collisions Collisions General Case

Unit 3, Lesson 6 Collisions

Collisions - General Case Newton’s 3 rd Law: F 1 = - F 2 F 1 Δt= - F 2 Δt Δp 1 = - Δp 2 Δp 1 + Δp 2 = 0 So total momentum of both objects is conserved! (assuming no outside forces!)

Collisions in One Dimension Trystan’s 1700 kg truck collides head-on with Jon’s 68000 kg tank, which is going west at 15 m/s. The wreckage sticks together and moves west at 13. 5 m/s just after the collision. (But Trystan is miraculously okay!) Find the initial velocity of Trystan’s truck. 15 m/s momentum before = momentum after ? 1700 v + 68000(-15) = (68000+1700)(-13. 5) 1700 v = 68000(15) + 69700(-13. 5) v = 46. 5 m/s = 167 km/h 13. 5 m/s

Practice: • Do #5 -7 and 12 on pg. 69 of your textbook. • When finished, use the rest of class to work on your lab reports (Atwood Machine and Pendulum Lab) and/or energy problems.

Unit 3, Lesson 7: Collisions in 2 D Ø Principle: Momentum is conserved in both “x” and “y” directions separately.

Example 1 A bus (15000 kg) going 10 km/h North and a garbage truck (10000 kg) going 30 km/h East collide at an intersection and stick together after colliding. Find the velocity of the combined wreckage just after they crash.

Solution • truck bus

Example 2 An 80 kg wide-receiver running 7. 0 m/s towards the end-zone is tackled by a 120 kg defensive-end going 6. 0 m/s across the field. Find the velocity of the 2 players just after contact.

Solution •

Brain Break!

Example 3 Jakob uses his knowledge of physics to become a pro pool player. His cue-ball, going 4. 0 m/s, hits an identical (except for colour) stationary 300 g ball. The cue-ball ends up going 3. 5 m/s at an angle of 30 to the original path. Find the final velocity of the other ball.

Solution

Practice: • Do #1 on your Momentum Problem Set.

Unit 3, Lesson 8: Explosion Problems A defective 20 kg land-mine explodes into 4 pieces which have the following velocities just afterwards. Find the velocity of the fourth piece. Mass Velocity A 7 kg 300 m/s N B 4 kg 500 m/s E C 5 kg 400 m/s 30 S of W D 4 kg ?

• Solution

Practice: • Explosions: #4 and 5 on your Momentum Problem Set, and #4 on pg. 79 of your textbook. • Collisions: #1, 2, 5, and 6 on pg. 78/79 of your textbook.

Unit 3, Lesson 9: Impulse Example 1 A ball is pitched at 20 m/s towards home (East). The 250 g ball is hit directly towards 1 st base at 30 m/s. Find the impulse (change in momentum) delivered to the ball.

Solution • θ

Example 2 A 250 kg satellite going 75 m/s is struck by a meteor and absorbs an impulse of 15000 Ns perpendicular to the direction of motion. Find the final velocity of the satellite.

Solution •

Brain Break!

Example 3 A 5000 kg meteor heads directly towards the Enterprise (47000 kg) at 600 m/s. The “tractor beam” diverts it so that it end up 15 off course at 530 m/s. Find: A) the impulse applied to the meteor B) the force exerted on the meteor if the force acts for 15 s

Solution to (a) •

Solution to (b)

Practice: • Do #2 and 6 -9 on your Momentum Problem Set (you can now do all of the problems on the sheet). • The test for this unit is on Monday. Use the problem sets and the review sheet to help you prepare!