There are some missing data in the text of the problem. I've found them online:
a) coefficient of friction dry steel piston - steel cilinder: 0.3
b) coefficient of friction with oil in between the surfaces: 0.03
Solution:
a) The force F applied by the person (300 N) must be at least equal to the frictional force, given by:

where

is the coefficient of friction, while N is the normal force. So we have:

since we know that F=300 N and

, we can find N, the magnitude of the normal force:

b) The problem is identical to that of the first part; however, this time the coefficienct of friction is

due to the presence of the oil. Therefore, we have:
<span>antimony. It has +3,+5,-3 so yeah. the others carbon+2,+4,-4, chlorine +1,+5,+7,-1 but -1 is the most often so it isn't Cl, calcium +2.</span>
Wind speed and air temperature are used to calculate a windchill factor.
<u>Explanation:</u>
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Wind-chill factor is the reduction of body temperature due to the passing flow of lower-temperature air.
The air temperature value is always higher than the wind chill numbers. the heat index will be used if the apparent temperature is higher than the air temperature.So, Wind speed and air temperature are mainly used to calculate a windchill factor.
There are many ways, the surface loses its heat through conduction, evaporation,radiation, and convection.The rate of convection depends on the difference in temperature between the surface and the fluid surrounding the surface and the velocity of that fluid with respect to the surface. The air around the warm surface will be heated, an insulating layer of warm air forms against the surface.The layer becomes a boundary between two. As the wind speed is high the surface cools down rapidly.