Answer to Question #1651 in Mechanics | Relativity for sk
A student applies an upward force of 56 N to a 5.6-kg physics textbook. Find the book’s acceleration (positive for up, negative for down).
There are two forces applied to the book, the downward gravitational attraction (mg = 5.6 *10 = 56N) and upward student's (F = 56 N), they are directed oppositely. The resultative force is equal to zero, so the acceleration equals to zero too.