A45.0 kg girl is standing on a 159 kg plank. the plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless surface. the girl begins to walk along the plank at a constant velocity of 1.38 m/s relative to the plank.
(a) what is her velocity relative to the surface of ice?
1 m/s
(b) what is the velocity of the plank relative to the surface of ice?
2 m/s

(a)

(b)

Explanation:

According to the law of conservation of momentum:

Initially, the girl and the plank are at rest. So, relative to the ice, we have:

(a) The velocity of the girl relative to the ice is:

Here, is the velocity of the girl relative to the plank and is the velocity of the plank relative to the ice.

Replacing (1) in (2):

(b) According to (2), the velocity of the plank relative to the surface of ice is:

The negative sing indicates that the plank is moving to the left.

the temperature and the pressure affect solubility. temperature affects by changing the properties of the solvent. the increase in pressure increases solubility, the decrease in pressure decreases solubility.

3. dark matter

empty space could also be a simple vacuum