Question

A 20.0 kg mass moving at a velocity of + 3.0 m/s is stopped by a constant force of 15.0 n. how many seconds must the force act on the mass to stop it? html editor keyboard shortcuts

Answer 1

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