A40.-kilogram mass is moving across a horizontal surface at 5.0 meters per second. what is the magnitude of the net force required to bring the mass to a stop in 8.0 seconds?

From newtons second law of motion the rate of change of linear momentum is proportional to the resultant force. Momentum is the product of mass and the speed of a body.
In this case Momentum is 40 kg × 5 m/s = 200 kgm/s
From the same law we deduce that impulse (Ft) is equal to the change in momentum. Therefore, Ft = change in momentum.
Hence, to get the impulsive force we divide the change in momentum by time.
 F = 200kgm/s ÷ 8 sec = 25 N
hence the force is 25 N