Explain why a flower vase falling on carpet is less likely to shatter than if it were to fall on a hard wooden floor.

Achieved “The wooden floor exerts a greater force on the vase” “The vase stops more suddenly on the wooden floor” Achieved with Merit “The wooden floor exerts a greater force on the vase BECAUSE it stops more suddenly” “The carpet exerts less force on the vase BECAUSE the cushioning means it takes longer to stop”

Achieved with Excellence “For both floor surfaces, the vase would experience the same change in momentum (Δp) BECAUSE they hit at the same speed and come to a stop. HOWEVER, the vase hitting the carpet will stop over a longer period of time, BECAUSE of the cushioning. SINCE Δp = F Δt, a longer stopping time THEREFORE means a smaller force is exerted on the vase to give the same change in momentum. A smaller force MEANS the vase is less likely to break.”

Example SIX Two balls A and B are about to collide. Ball A’s momentum is 8.0 kgms -1 (→) and Ball B’s is 5.0 kgms -1 (←). After collision, both balls move in opposite directions, ball A having a momentum of magnitude 1.5 kgms -1 (←). a)Calculate the total momentum b)Calculate the momentum of ball B after the collision c)Calculate the velocity of ball B after the collision, if its mass is 300 g

Example SEVEN A Morris Minor car (mass 750 kg) is travelling at 30 ms -1 and collides head-on with a Mercedes Benz car (mass 1600 kg) travelling at 20 ms -1 in the opposite direction. The two cars lock together in the crash. a)Calculate the total momentum b)Calculate the velocity of the combined wreck after the collision c)Why does this velocity quickly reduce to zero?

DO NOW Activity 10A (green book, pg. 123) Questions 1, 2, 3 and 6 only Homework Booklet Worksheet TEN & ELEVEN NCEA 2010 up to page 7 Activity 10B (green book, pg. 128) Questions 3 and 5 EXTENSION: Activity 10B All Qs