Anwser
The strength of a force is usually expressed by its magnitude. We have also to specify the direction in which a force acts.
you can increase kinetic thermal energy of the water by boiling it.
Answer:
Velocity after collision will be 20 m/sec
Explanation:
We have given mass of arrow 
Mass of arrow 
Mass of apple 
Apple is at rest so velocity of apple 
According to conservation of momentum
Momentum before collision is equal to momentum after collision



v = 20 m/sec
If a body is moving from left to right or right to left it is linear motion in x- direction. It is also called one dimensional motion.
If a body is moving up to down or down to up it is linear motion in y- direction. It is also called one dimensional motion.
But if a body is moving forward as well as downward it travels in X direction and in y direction at the same time. Such a motion is called two dimensional motion.
E.g motion of a ball.
Attachment shows path of two dimensional motion of a ball.