Everything Science Grade 12

6.5 CHAPTER 6. MOTIONIN TWO DIMENSIONS

• An elastic collision isa collision where bothmomentum and kineticenergy is
  conserved.

pbefore = pafter

KEbefore = KEafter

• An inelastic collision iswhere momentum is conserved but kinetic energy is not
  conserved.

pbefore = pafter

KEbefore �= KEafter

• The frame of referenceis the point of view fromwhich a system is observed.

Chapter 6 End of Chapter Exercises

1. [IEB 2005/11 HG] Two friends, Ann and Lindiwe decide to race each
   other by swimming across a river to the otherside. They swim at
   identical speeds relativeto the water. The river has a current flowing
   to the east.

N

S

W E

�

��

start

finish

Ann Lindiwe

current

Ann heads a little westof north so that she reaches the other side

directly across from thestarting point. Lindiwe heads north but is car-

ried downstream, reaching the other side downstream of Ann. Who

wins the race?

(a) Ann

(b) Lindiwe

(c) It is a dead heat

(d) One cannot decidewithout knowing the velocity of the current.

2. [SC 2001/11 HG1] Abullet fired vertically upwards reaches a maxi-
   mum height and falls back to the ground.