A ball of mass m moving with speed V collides with another ball of mass 2m (e= 1/2) in a horizontal smooth fixed circular tube of radius R (R is sufficiently large R>>>d). The time after which next collision will take place is:

Aswimmer is determined to cross a river that flows due south with a strong current. initially, the swimmer is on the west bank desiring to reach a camp directly across the river on the opposite bank. in which direction shoud the swimmer head? a. the swimmer should swim southeast. b. the swimmer should swim south. c. the swimmer shuold swim northeast. d. the swimmer should swim due north. e. the swimmer should swim due east.