An arrow of 43 g moving at 84 m/s to the right, strikes an apple at rest. The arrow sticks to the apple and both travel at 16.8 m/s after impact. What is the mass of the apple? Plz help ASAP I will give you 40 points

You throw a ball upward and let it fall to the ground. your friend drops an identical ball straight down to the ground from the same height. is the change in kinetic energy (from just after the ball is released until just before it hits the ground) of your ball greater than, less than, or equal to the change in kinetic energy of your friend's ball?