Question

A 1400 kg car is moving at 33.8 m/s when a force is applied the opposite direction of the car's motion. The car slows down to 21.4 m/s . the force is applied for what is the magnitude of the force?

Answer 1

Solve for acceleration:

a = (21.4 m/s - 33.8 m/s) / (4.7 s)

a ≈ -2.6 m/s²

Solve for force:

F = (1400 kg) a ≈ -3700 N

The minus sign tells you the force points in the opposite direction of the car's motion. Its magnitude is always positive, so F = 3700 N.