In which of the following statements is a net force of zero acting on the object in question?
A. A car drives around a circular racetrack at a constant speed
B. A person pushes on a door to hold it shut
C. A ball, rolling across a grassy field, slowly comes to a stop
In which of the following statements is a net force of zero acting on the object in question?
A. A car drives around a circular racetrack at a constant speed
B. A person pushes on a door to hold it shut
C. A ball, rolling across a grassy field, slowly comes to a stop
The correct option is B B only
A net force of zero is acting on an object if that object maintains a constant velocity. The car going around the racetrack in statement A has a constant speed, but since its direction is constantly changing (as it’s going in a circle), its velocity is also changing, and so the net force acting on it isn’t zero.
The person in statement B exerts a force on the door, but neither she nor the door actually moves: the force is exerted so as to hold the door in place. If the door isn’t moving, its velocity is constant at zero, and so the net force acting on the door must also be zero.
Though no one is pushing on the soccer ball in statement C, some force must be acting on it if it slows down and comes to a stop. This is a result of the force of friction between the ball and the grass.
Since the net force is zero only in statement B, B is the correct answer.
B only
A net force of zero is acting on an object if that object maintains a constant velocity. The car going around the racetrack in statement A has a constant speed, but since its direction is constantly changing (as it’s going in a circle), its velocity is also changing, and so the net force acting on it isn’t zero.
The person in statement B exerts a force on the door, but neither she nor the door actually moves: the force is exerted so as to hold the door in place. If the door isn’t moving, its velocity is constant at zero, and so the net force acting on the door must also be zero.
Though no one is pushing on the soccer ball in statement C, some force must be acting on it if it slows down and comes to a stop. This is a result of the force of friction between the ball and the grass.
Since the net force is zero only in statement B, B is the correct answer.
