A raft of mass 180kg carries two swimmers mass of 50kg and 80kg. The raft is initially floating at rest. The two swimmers simultaneously dive off opposite ends of the raft each with a horizontal velocity of 3 m/s. With what velocity in in which direction does the raft start to move

3 m/s to the right

Explanation:

Assuming swimmer 1 is at the left of the raft and swimmer 2 is at the right (as shown in the figure), we can make a Free body diagram and find in which direction is the greatest exerted horizontak force on the raft:

Where:

Being the mass of swimmer 1 and the acceleration due gravity

Being the mass of swimmer 2  

Then:

(1)

(2)

Comparing both forces, and taking into account each swimmer has a horizontal velocity of , we can deduce the raft will move in the direction of the greatest force, which is where swimmer 2 is (to the right).

It equals just about 6,300 km per hour each day an week

W= fd
where f is an applied force and d is the distance over which it is applied. when a parachuting skydiver is at constant velocity, he is experiencing "terminal velocity", the point at which his acceleration down is canceled out by air resistance. that means that the resisting force of the air is equal to his weight, but in the opposite direction. with this, we can solve for the work done by the force.
w = fd
w = (92.0)(9.81 m/s^2) (325)
w= 2.93 x 10^5 j
the value for work in this case is positive because it is pushing up on the skydiver, who has a downward force of gravity.
therefore the answer is 2.93 x 10^5 j