17. The SI unit for force is N.
18. When an Unbalanced force acts upon and object, the object will change speed and/or direction of motion.
19. Average speed is the speed averaged over a span of time. Instantaneous speed would be the speed at any given instance during that span of time.
20. Acceleration= (final velocity - initial velocity) / time
Final velocity= 0 m/s
Initial velocity= 25 m/s
Time = 40 sec.
So, acceleration (0 - 25) m/s / 40 sec.
Acceleration = -0.625 m/s^2
