Answer:
Step-by-step explanation:
Given
mass of Daniel

mass of Rebecca

Initial velocity of daniel

Initial velocity of rebecca

Let us suppose velocity of Daniel is v m/s at an angle of \theta w.r.t horizontal
conserving Momentum in Horizontal direction


------1
Conserving momentum in y direction

---------2
divide 1 & 2



substitute the value of \theta in equation 2


(b)Change in kinetic Energy of Rebecca

