When a sailor jumps from a boat to the river bank?

A boat is pushed away from the river bank when a sailor jumps from the boat to the bank. Why?

If a man jumps out from a boat, the boat moves backwards. Why?

If a man jumps out from a boat, the boat moves backwards. Why?

In a river flowing at 20 m//s , a swimmer who can swin at 10 m//s relative to water jumps from on bank of the river. The direction from normal to the bank of river at which swimmer should swim so as to minimize the drifts is (pi)/(x) rad. Then x is

The river 500 m wide is flowing with a current of 4kph. A boat starts from one bank of the river wishes to cross the river at right angle to stream direction. Boatman can row the boat at 8 kph. In which direction he should row the boat. What time he ''ll take to cross the river ?