Two boxes of masses m and 3m are stacked as shown in the figure. the contact between the more massive box and the underlying horizontal surface is smooth (frictionless) and the surface between the boxes is rough. if the upper box does not slide on the lower one, what is the static friction force on the upper box?
a. f.
b. f/2.
c. f/3.
d. f/4 m.

Complete these sentences. if a roller coaster train has a potential energy of 1,500 j and a kinetic energy of 500 j as it starts to travel downhill, its total energy isj. once the roller coaster train gets closer to the bottom of the hill, its kinetic energy increases to 1,100 j, and its potential energy decreases to j. when the train reaches the bottom of the track and is traveling along the ground, its kinetic energy isj.

According to the image below, which season is about to begin in the southern hemisphere? a. summer b. autumn c. winter d. spring

Which inventor was often called the lady edison