Fnet=ma Problems

Question

1) a 500 kg car is travelling at 15 m/s and experiences a forward engine force of 2000N for 3 seconds. The combined frictional forces acting on the car are 600 N. What is the car's acceleration?

2) Four people are pushing on a box where the box has no friction but their feet do. Person #1 pushes with 22N to the right, person #2 with 14 N to the right, and and person #3 pushes with 30 N to the right. Person #4 pushes with 72 N to the left. The box has a mass of 5 kg; determine acceleration.

3) Edward applied a horizontal force to stop a pickup truck that was sliding toward Bella. Find the magnitude of the horizontal force needed, if the truck, going from an initial speed of 14 m/s, stopped over a distance of 1.0 m (the length of Edward's arms). The truck's mass is 1600 kg.

Answer 1

1. F_net = m*a = 2000 - 600 = 500*a, solve for a
2. F_net = 22 + 14 + 30 -72 = -6N or just 6N to the left so 6 = m*a so acceleration is 6/5 or 1.2 m/s² to the left
3. F*d = Change in kinetic energy, we want it to stop so change is the current kinetic energy (like if you have 5 joules of energy and need to stop thats a change of 5 joules to get to zero joules) so

So F*1 = 0.5*1600*(14²) so solve for F