You're sitting in the back of a taxi and place your bag on the seat next to you. The taxi enters a traffic circle and travels the circle at a constant speed. During this motion, you notice that your bag does not move relative to the seat. As the taxi travels the traffic circle, which of the following statements are true in an inertial reference frame?

I. The acceleration of the bag is nonzero and constant.
II. The net force on the bag is nonzero and constant.
III. The frictional force acting on the bag is nonzero and constant.

(a) II only
(b) II and III
(c) I, II, and III
(d) III only
(e) None of the statements (I, II, or III) are true.

(d) III only

Explanation:

We have to observe the motion of the bag with respect to taxi , considering taxi as stationary or inertial frame . Since bag is not moving with respect  to taxi , the inertial frame that means , net force on it is zero .So option i and ii are ruled out .

Now how to explain motion of the bag ie why it is stationary ie what are the balancing force acting on it. We know that on a body on circular path , a force called centripetal force is acting on it . So that force must be acting on it . The balancing force is the frictional force which is keeping it stationary with respect to taxi . Hence the third option is correct.

powerful computers now, not then