Ball B, moving in the positive direction of an x axis at speed v, collides with stationary ball A at
the origin. A and B have different masses. After the collision, B moves in the positive direction
of the y axis at speed v/4 (a) In what direction does A move? 11.3 xcounterclockwise from the
+x axis (b) Show that the speed of A cannot be determined from the given information. (Select
all that apply.) O The initial speed v is unknown The final direction of A is unknown. O The
final position of A is unknown. The mass of A relative to the mass of B is unknown. O The final
position of B is unknown Additional Materials Section 9.8
Solution
Solution- As we know that momentum is conserved.
Initially no momentum along the y-axis, Therefore A has the opposite y momentum from B.
m_A v_y_A = m_B v/3
v_y_A = (m_B / 3m_A) v
There WAS momentum along the y-axis, and B takes none of that, so A has all of its original
x  momentum .
m_A v_x_A = m_A v
v_x_A = v
The angle is related to the x and y components of velocity:
tan ? = v_y_A / v_x_A
? = arctan (m_B / 3m_A)
We can find direction as
?=arctan(1/4)
=14.04
b) Here negative sign says that angle is clockwise below the x-axis from the above equation it is
clear that to find the velocity of A, we need the mass of A and B Hence the given information is
not sufficient.