Physics Answers

A spring with a spring constant of 25 N/m is stretched 65 cm. What was the magnitude of the force used?

An electric wire in the wall of a building carries a current of 25A vertically upward. What is the magnetic field due to this current at point P 10cm due north of the wire

A 100 kg wooden crate is at rest on a level stone floor. If the coefficient of static friction is 0.5. what is the minimum horizontal force needed to get the box moving

Oxygen ( molecular weight 32) is compressed reversibly and polytropically in a cylinder

from 1.05 bar, 15oC to 4.2bar in such a way that one- third of the work input is rejected

as heat to the cylinder walls . calculate the final temperature of the oxygen. Assume

oxygen to be a perfect gas and take Cv = 0.649kJ/kg.K

0.05 kg of carbon dioxide (molecular weight 44), occupying a volume of 0.03m3 at

1.025bar , is compressed reversibly until the pressure is 6.15bar. calculate the final

temperature the work done on the CO2 and the heat flow to or from the cylinder walls ,

1- when the process is according to the law p.ν1.4 = constant , 2- when the process is

isothermal , assume carbon dioxide to be a perfect gas , and take γ = 1.3

Is sitting on a chair considered work

A 10 kg block is allowed to slide down a frictionless 60⁰ incline. What is the block's acceleration?

take g = 9.8m/s²

A body with mass 600 kgis located on a 30 degressinclined plane. Calculate the pulling force without friction.

take g = 9.8m/s²

Oxygen, O2, at 200 bar is to be stored in a steel vessel at 20oC the capacity of the vessel

is 0.04m3

. Assuming that O2 is a perfect gas, calculate the mass of oxygen that can be

stored in the vessel. The vessel is protected against excessive pressure by a fusible plug

which will melt if the temperature rises too high. At what temperature must the plug

melt to limit the pressure in the vessel to 240bar? The molecular weight of oxygen is 32

(10.5 kg; 78.6oC)

A heat exchanger wall consists of a copper plate 20 mm thick. The heat transfer

coefficients on the two sides of the plate are 2700 and 7000 W/m2K, corresponding to

fluid temperatures of 92 °C and 32 °C, respectively. Assuming that the thermal

conductivity of the wall is 375 W/mK,

a. Calculate the surface temperatures in °C, and

b. Calculate the overall heat transfer in W/m2K.