The mass is 20 kg, initial speed is 30 m/s and the final speed is 0 m/s (rest),
while the force is 15 N
Using second newton's law of motion which states that the rate of change in momentum is directly proportional to the resultant force. Then
Ft = MV-MU
15 t = 20 (0-3)
15t = -60
t = -4 sec ( negative because the force is acting on opposite direction to the motion)
Therefore, the time taken is 4 seconds
