Which of the following carts is experiencing an unbalanced force?

Question

Which of the following carts is experiencing an unbalanced force?

 

Multiple Choice:

A) A cart that is accelerating

B) A cart that is traveling at a constant speed

C) A cart that is at rest

D) Both A and B

E) All of the above

 

I KNOW THE ANSWER IS A. BUT, WHY? PLEASE EXPLAIN.

Answer 1

The question needs to be rephrased, as there may possibly be two answers, A or B. If the words " constant speed' are changed to "constant velocity", Then A is correct. If no direction is associated with the constant speed as is the case in the question, then it is possible that the object is accelerating, since it could be going around a curve at constant speed, in which case the answer could possibly be B. If the question were to ask "Which of the following carts must be experiencing an unbalanced force?", then the answer is A.

Answer 2

The first Newton's Law states that an object either remains at rest or continues to move at a constant velocity, unless acted upon by an external force.

A is the only one accelerating, so it's the only one experiencing an unbalanced force.

Answer 3

In a cart experiencing all forces in balance, the net force on the cart is 0.  If F=0, then by F=ma, a=0.  If the cart in Answer A is accelerating, then the acceleration cannot equal 0. Therefore, it must be experiencing an unbalanced force.