URGENT: Two horizontal forces act on an object on a surface. There is a 20 Newton applied force to the left and a sliding frictional force of 5 Newtons to the right. What is the net force on the object?

A248-g piece of copper is dropped into 390 ml of water at 22.6 °c. the final temperature of the water was measured as 39.9 °c. calculate the initial temperature of the piece of copper. assume that all heat transfer occurs between the copper and the water. remember, the density of water is 1.0 g/m

Idon’t quite understand this problem

How can waves travel through ground?