Ph202H/212H
W09 Homework # 2 – due Thursday, January 8
1. Two objects (A and B) collide. A has mass 2.0 kg and B has mass 3.0 kg. The
velocities before the collision are viA = <15,30> m/s and viB = <-10,5> m/s. After the
collision, vfA = <-6,30> m/s. Find the final velocity of B and the change in kinetic energy
in the collision.
Ans: -315 J
2. A helium atom (m = 6.6465 × 10−27 kg) collides elastically with an oxygen atom (m =
2.6560 × 10−26 kg) at rest. After the collision, the helium atom is observed to be moving
with a velocity of 6.636 × 106 m/s in a direction at an angle of 84.7° relative to its
original direction. The oxygen atom is observed to move at an angle of −40.4°. (a) Find
the speed of the oxygen atom. (b) Find the speed of the helium atom before the collision.
Ans: (b) 8.376 × 106 m/s
3. An atom of mass m1 = m moves in the positive x direction with speed v1 = v. It collides
with and sticks to an atom of mass m2 = 2m moving in the positive y direction with speed
v2 = 2v/3. Find the resultant speed and direction of motion of the combination, and find the
kinetic energy lost (as a fraction of the initial total kinetic energy) in this inelastic collision.
Ans: 53.1°; 51%