Question

When you push a 1.91-kg book resting on a tabletop, you have to exert a force of 2.11 N to start the book sliding. Once it is sliding, however, you can use a force of only 1.04 N to keep the book moving with constant speed.

Answer 1

To start a book sliding on a table, a force greater than the static friction must be applied (2.11 N). Once moving, a smaller force overcomes kinetic friction to maintain velocity (1.04 N). Newton's second and third laws are used to analyze various force interactions and calculate work.

Step-by-step explanation:

When you push a book across a table and the book starts to slide, it's due to overcoming static friction, which requires a force of 2.11 N. Once the book is in motion, only 1.04 N is required to maintain a constant speed because kinetic friction is less than static friction. Pushing the book with a force of 2 N across a distance of 0.5 m results in 1 Joule of work, since work is the product of force and displacement in the direction of the force.

The table exerts an upward force, known as the normal force, on the book. This normal force can be found by multiplying the mass of the book by the acceleration due to gravity (1.91 kg × 9.8 m/s² = 18.71 N). However, due to the wording in the reference, we're informed that the desk exerts an upward force of 32 N. Using Newton's laws, specifically Newton's second law (F = m × a) and Newton's third law (for every action, there is an equal and opposite reaction), allows us to analyze the forces at play.

For example, lifting a 20 N book down from a shelf 1 m vertically equates to -20 Joules of work done by gravity as the book is being moved with a downward motion.