Billy stands on a hill without slipping. In which direction is the force of friction acting? A. along the surface of the hill, toward the bottom of the hill.
B. perpendicular to the surface of the hill
C. straight up
D. Along the surface of the hill toward the top of the hill.

The membrane surrounding a living cell consists of an inner and an outer wall that are separated by a small space. assume that the membrane acts like a parallel plate capacitor in which the effective charge density on the inner and outer walls has a magnitude of 7.0 × 10-6 c/m2. (a) what is the magnitude of the electric field within the cell membrane? (b) find the magnitude of the electric force that would be exerted on a potassium ion (k+; charge = +e) placed inside the membrane.

25pts the diagram shows the positions of the sun, moon and earth during spring tides, when the high tides are at their highest and low tides at their lowest. what is it about these positions that causes these high and low tides?

If a balloon is taken outside on a very cold day, what will occur?