Competency #11 & #1
Answer and Explanation
A fan-cart travels across the floor. It's is shown below:
Which of the following force diagrams is possible, based on Newton's 1st Law (there may be more than one correct answer)?
Answer:
Force diagrams B and C are possible.
Newton's first law says that an object moves with a constant velocity if and only if the net force acting on the object is zero. The first law can also be stated as “Every object continues in a state of rest, or in a state of motion in a straight line at constant speed, unless it is compelled to change that state by the forces exerted upon it.” (Hewitt et al)
By looking at the position versus time graph, we see that the fan-cart is moving away from the sensor. We also see that the fan-cart is moving faster at the end than at the beginning. This means that its speed and velocity have changed. Therefore, by either statement of the first law above, the object must have a non-zero net force. Only force diagrams B & C have non-zero net forces. The net force in both cases is to the right.