Astack of books is sitting on a table. what force is pulling downward on it

Atrain departs from its station at a constant acceleration of 5 m/s. what is the speed of the train at the end of 20s?

Waves that cause the most damage during an earthquake are a. surface waves c. s waves b. p waves d. ocean waves

Two forces produce equal torques on a door about the door hinge. the first force is applied at the midpoint of the door; the second force is applied at the doorknob. both forces are applied perpendicular to the door. which force has a greater magnitude?