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.

Protons have a positive charge and, collectively, give an element its atomic number.

Inner peace.. jk it's  a stable electron configuration

How is it possible that phylogenies based on sequences from nuclear genomes and organellar genomes (i.e., chloroplasts and mitochondria) from the same group of species yield phylogenetic trees with different branching orders?   answer :   the genome of the endosymbiont is more closely related to members of the group in which it originally evolved, while the nuclear genome of the engulfing organism has its own evolutionary trajectory.