Hey guys.. ans me
a swimmer reaches the other bank of flowing river exactly opposite to the starting pt. if he was swimming at 2 kmh while maintaining 150 degree with the flow
then time taken by him to cross the river if 1km wide

The time taken by the swimmer was 1 hour.

Why?

Since the swimmer is maintaining an angle of 150° while he was swimming, there were two components of the speed (horizontal and vertical). If we want to calculate the time taken by him to cross the river, we need to calculate the vertical speed and consider that the flow's speed is compensated by his horizontal speed.

We can calculate both components of the speed using the following formula:

Now, calculating we have:

Therefore, we have that the horizontal speed is compesating the flow's speed while his vertical speed is used to cross the river which is 1 Km wide.

Hence, we have that the tame taken is:

Have a nice day!

the answer is b, have negligible mass