(b) Let the string now have length 2l with a mass m on the end. Let another mass m be positioned next to the l mark on the string but not touching the string (see Figure). The right mass is released. It heads toward the wall (while the other mass is still motionless) and then sticks to the other mass to make one large blob which then heads toward the wall.17 How much time does this whole process take?18
(c) Let there now be N masses and a string of length N l (see Figure). How much time does this whole process take?
(d) Consider now a massless bucket at the end of the string (of length L) which gathers up a continuous stream of sand (of total mass M) as it gets pulled to the wall (see Figure). How much time does this whole process take? What is the mass of the contents of the bucket right before it hits the wall?