For a closed thermodynamic system of constant composition, specify the natural variables of the following state functions and write down an equation for the complete differential of the state function with respect to the natural variables. (i) internal energy u. enthalpy h. helmholtz free energy f. [1 mark] [1 mark] [1 mark] (iii) (b) using the first and second laws of thermodynamics, the equations from part (a), equations relating enthalpy and, separately, helmholtz free energy to internal energy and the maxwell relation for helmholtz free energy, derive an expression for the partial derivative of enthalpy with respect to volume at constant temperature in terms of temperature, volume and pressure. [5 marks] using the result from part (b), explain which physical properties of a pure substance should be measured to calculate the change in enthalpy with a change in volume at constant temperature.

the box does not move because you need to use a force greater than 300 n. you are only using 50 n. it needs to at least be 301 n for the box to move because then it is an unbalanced force and it will move the way that the greater force is pushing it. if you use only 300 n it will be a balanced force and will not move because the force you are exerting on the   box is the same as its force.

hope this !

im sorry if i went too in depth, i am going to include a link to a video on khan academy that will explain this.   hope that you like the video and that it explains more in detail to you.

that is the link.

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia