A 70 kg hockey player moving at 5 m/s collides with a 90 kg hockey player initially at rest. Which experiences a greater acceleration?

Every action has an equal and opposite reaction. (Newton's third law) so the FORCES on each are the same.

F=ma ( Newton's second law)

so a = F/m -> the larger mass has the lower MAGNITUDE of acceleration.

Now if you include the direction then one is positive and one is negative. And a positive is always greater than a negative. But that isn't what you wanted for your answer.

We can assume this problem happens in one-dimension, with the 70 kg hockey player moving to the positive x.

We don't really need any math, because intuitive sense tells us that the lower mass player will rebound slightly (going from a high positive velocity to a low negative velocity) while the high mass player will go from rest to a low positive velocity.

To visualize this crudely:

o ---> O

<-- o O ->

Since acceleration is defined as a change in velocity, and the low mass player is going from +5 m/s to around -2 m/s, and the high mass player going from 0 m/s to +1 m/s (remember 2 and 1 are only estimates), we can say the 70 kg player will accelerate more.