Question

Suppose you slowly and at constant speed lift a 4 N book from the floor to a shelf 2 m above the floor.

(a) While your lifting it the net force on the book is zero(True,False)

(b) While your lifting it the force by your hand against the book is 4 N(True,False)

(c) The net work done on the book is zero(True,False)

(d) The work done by your hand on the book is 8 Joules(True,False)

(e) The net work done by the gravitational force is minus 8 Joules(True,False)

Answer 1

a as the book is slowly lifted,it is moving at a constant speed in upwards direction,hence net force on it will be zero(true)

b force applied by the hand on the book will be equal to the weight of the book(true)

c since the kinetic energy of the book remains constant as it is having a constant speed,therefore net work done on it will be zero according to the work energy theorem(true)

d force applied by the hand=4 newtons

displacement of the book =2 meters

angle between force and displacement=0 degrees

therefore work done=Fd=4*2=8 joules(true)

e as the net work done on the book is zero,therefore work done by gravity must be equal to -8 joules(true)

Answer 2