Question

. While a person lifts a book of mass 2 kg from the floor to a tabletop, 1.5 m above the floor, how much work does the the person do on the book? How much work does gravity do on the boo

Answer 1

Answer:

a) 29.4 J

b) - 29.4 J

Explanation:

Given:

Mass of the book, m = 2 kg

Height above the floor, h = 1.5 m

Now,

the work done by the person will be = Force applied on the book × displacement of the book

thus,

Work done by the person = mg × h

where, g is the acceleration due to gravity

thus, on substituting the values, we get

Work done by the person = 2 × 9.8 × 1.5 = 29.4 J

now,

for the force applied by the gravitational pull (downwards) the displacement is in opposite direction (upwards) to the force of the gravity.

Thus,

work done by the gravity will be negative

therefore, the work done by the gravity = - mg × h

or

work done by the gravity = - 29.4 J

Answer 2

Answer:

29.4 J  -29.4 J

Explanation:

The work done by the person on the book is given by =mgh

where m =mass

          g= acceleration due to gravity

          h=height

Here m=2 kg given g=9.8 kg m/$sec^2$ h=1.5 meter

So work done by the person =2×9.8×1.5=29.4 J

As the gravitational force work downward and person lift the book upward so work done by gravity = -mgh = -2×9.8×1.5=  -29.4 J