9.) A 40-kg bookshelf requires a 200 N force to begin its motion. Once moving. It only requires a force of 50 N.
a. What is the normal force?
b. Determine the static coefficient of friction

Abearing is designed to a reduce friction b. support a load c.guide moving parts such as wheels, shafts and pivots d. all of the above

To do work, this truck uses energy stored in chemical fuel and an electrical battery. how much total energy does this truck put out?

The freezing and boiling point of a substance changes as the air pressure around it changes. for example, at a lower air pressure (higher altitude) it is easier for water molecules to escape from liquid into the air. in a high altitude city such as denver, colorado compared to a sea-level city such as houston, texas, water