what does it mean to have a net force of zero? what are the only causes in which an object can have a net force = 0?

How much force must a locomotive exert on a 12840-kg boxcar to make it accelerate forward at 0.490 m/s2?

2.22/3.33 points | previous answers tamucolphysmechl1 4.pre.002. ask your teacher my notes question part points submissions used on a frictionless air track, a blue glider with mass 0.200 kg is moving to the right with a speed of 8.00 m/s. it strikes a red glider that has mass 0.600 kg and that is initially at rest. after the collision, the blue glider is moving to the left with a speed of 2.40 m/s. (a) what are the magnitude and direction of the velocity of the red glider after the collision? magnitude 3.33 m/s correct: your answer is correct. direction correct: your answer is correct. (b) is this collision elastic?

Could someone . i have tried to solve myself but my calculation is off