Answer:
Step-by-step explanation:
Work done by janitor = increase in potential energy of book
Potential energy = mgh , m is mass , h is displacement in height and g is acceleration due to gravity .
here displacement in height of book = 2.6 - 1.3 = 1.3 m
so h = 1.3 m
m = mass of the box
increase in potential energy of box = m x 9.8 x 1.3
= 12.74 m
Work done by janitor = 12.74 m Joule .