1. PHY 231 1 PHYSICS 231 Lecture 14: Collisions II: The momentum strikes back. Remco Zegers Walk-in hour: Thursday 11:30-13:30 am Helproom

2. PHY 231 2 Types of collisions Inelastic collisionsElastic collisions Momentum is conserved Some energy is lost in the collision: KE not conserved Perfectly inelastic: the objects stick together. Momentum is conserved No energy is lost in the collision: KE conserved Conservation of momentum: m 1 v 1i +m 2 v 2i =m 1 v 1f +m 2 v 2f Conservation of KE: ½m 1 v 1i 2 +½m 2 v 2i 2 =½m 1 v 1f 2 +½m 2 v 2f 2 (v 1i -v 2i )=(v 2f -v 1f ) Conservation of momentum: m 1 v 1i +m 2 v 2i =(m 1 +m 2 )v f

3. PHY 231 3 problem m 1 =5 kg m 2 =10 kg. M 1 slides down and makes an elastic collision with m 2. How high does it go back up?

4. PHY 231 4 Transporting momentum

5. PHY 231 5 Carts on a spring track K=50 N/m v 0 =5.0 m/s m=0.25 kg What is the maximum compression of the spring if the carts collide a) elastically and b) inelastically?

6. PHY 231 6 Impact of a meteorite Estimate what happens if a 1-km radius meteorite collides with earth:a) Is the orbit of earth around the sun changed? b) how much energy is released? Assume: meteorite has same density as earth, the collision is inelastic and the meteorites v is 10 km/s (relative to earth)

7. PHY 231 7 Playing with blocks m 1 =0.5 kg collision is elastic m 2 =1.0 kg h 1 =2.5 m h 2 =2.0 m A) determine the velocity of the blocks after the collision b) how far back up the track does m 1 travel? C) how far away from the bottom of the table does m 2 land d) how far away from the bottom of the table does m 1 land

8. PHY 231 8 Determine the velocity of the blocks after the collision m 1 =0.5 kg collision is elastic m 2 =1.0 kg h 1 =2.5 m h 2 =2.0 m

9. PHY 231 9 How far back up does m 1 go after the collision? m 1 =0.5 kg collision is elastic m 2 =1.0 kg h 1 =2.5 m h 2 =2.0 m v 1f =-2.3 m/s v 2f =4.7 m/s

10. PHY 231 10 How far away from the table does m 2 land? m 1 =0.5 kg collision is elastic m 2 =1.0 kg h 1 =2.5 m h 2 =2.0 m v 1f =-2.3 m/s v 2f =4.7 m/s h 1 =0.27 m (after collision back up)

11. PHY 231 11 How far away from the table does m 1 land? m 1 =0.5 kg collision is elastic m 2 =1.0 kg h 1 =2.5 m h 2 =2.0 m v 1f =-2.3 m/s v 2f =4.7 m/s h 1 =0.27 m (after collision back up) x 2 =2.96 m

12. PHY 231 12 The next joyride: Rotational motion!