Question

Gina pushes a book across a table at constant speed. Fatima lowers a book from a high shelf down to her waist, where it comes to rest. Isidra holds a book at her waist while carrying it up stairs. Jin holds a book at her waist while carrying it across the room at constant speed. Who does zero work on their book?

A. Gina

B. Fatima

C. Isidra

D. Jin

Answer 1

Gina pushes the book across the table. The direction of displacement ( either towards the right side or towards the left side) and the direction of force ( i.e. the weight of the book) are perpendicular to each other. Thus, Gina does zero work on her book.

Fatima lowers a book from a high shelf down to her waist. The direction of displacement of the book and the force ( the weight of the book) on it are acting along the same line ( i.e in the downward direction). Fatima has to do some work (which is not zero).

Isidra holds a book at her waist while carrying it upstairs.  The direction of displacement of the book (upward) and the force ( the weight of the book) on it  ( in the downward direction) are acting in the opposite direction. Isidra has to do some work (which is not zero).

Jin holds a book at her waist while carrying it across the room. If the there is no vertical displacement of the book, the direction of displacement ( either towards the right side or towards the left side) and the direction of force ( i.e. the weight of the book) are perpendicular to each other. Thus, JIn does zero work on her book.

Option (A) and (D) are correct.