QUESTION: "A 10-m-long glider with a mass of 680 kg (including the passengers) is gliding horizontally through the air at when a 60 kg skydiver drops out by releasing his grip on the glider. What is the glider's speed just after the skydiver lets go?" My problem here is that I do not understand what this problem is got to do with the length of the glider since the force is not asked, nor it does not seem to be needed. My solution is based on the change in the momentum: m1*v1 = m2*v2 and 680kg * 30m/s = (680-60)kg * v2 and I find v2=32.9m/s and our on-line system says it is incorrect. What's wrong/missing in my solution? Thanks.