Aman is crossing a river of width 100 m on a motorboat. the velocity of the motor boat is 4 m/s eastward and the velocity of the water current is 3 m/s northward. what is the resultant velocity of the boat and how much time will it take for the man to reach the other shore of the river? a) the resultant velocity of the motor boat is 5 m/s and it takes 20s to cross the river. b) the resultant velocity of the motor boat is 25 m/s and it takes 5s to cross the river. c) the resultant velocity of the motor boat is 6 m/s and it takes 20s to cross the river. d) the resultant velocity of the motor boat is 4 m/s and it takes 33s to cross the river.

By the Pythagorean theorem we get . Thus the resultant velocity will be 5 m/s.

However there is a typo in the choices. It should take 25 seconds to cross the river, not 20 seconds, since the boat actually travels 125 meters due to the water current, and 125/5 = 25 seconds.

Alternatively  you can calculate the eastward component of travel and get 100 / 4 = 25 seconds.

f=ma newton's second law 7x8=56n

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.