Question 1: A man trailing a trolley bag and suddenly, the wheels of the trolley bag get locked. The man realises that he has to put extra effort to drag the bag. The man finds it difficult to drag the bag because

Answer: Because of the friction force acting directly on the bag.

Explanation:

The function of the wheels is diminish the effect of the friction force, when the friction pulls back, it makes the wheel rotate, and this force is not applied directly on the bag.

Now the wheels are not working, so now the friction is acting directly on the bag, this is why the mand finds more difficult to drag the bag.