21. A uniform bar \( A B \) of length 6 as been placed on a horizontal smooth table of width \( 5 a \) as shown in the figure. Length \( 2 a \) of the bar is overhanging. Mass of the bar is \( 4 m \). An insect of mass \( 3 m \) is sitting at the end \( A \) of the bar. The insect walks along the length of the bar to reach its other end \( B \).

(c) When the temperature reaches \( -18^{\circ} \mathrm{C} \), the pressure of the gas in the cylinder is still equal to that of the atmosphere. Explain, in terms of the particles of the gas, how the pressure remains equal to its original value. Explain, in terms of the particles of the metal, why the decrease in the volume of the metal is less than that of the gas. decrease in the volume of the metal is much less than the decrease in the volume of the gas.

iii). Given that the cuboid has a mass of 700 g , Find its density in \( \mathrm{Kgm}^{-3} \)

EXERCISES It is known that the flow of fluid \( (\mathrm{Q} \) rate) is a fluid volume passing per unit time, based on the pressure gradient \( (\mathrm{P} / \ell) \) where \( (p) \) is the pressure between the ends of the tube flow stream, \( (\ell) \) is the length of pipe flow, also depends on the viscosity of the liquid \( (\eta) \) and the radius of the tube \( (r) \), by using the concept of compatibility between the units and dimensions theory derive a mathematical formula for flow rate depending on the variables mentioned above.

Train moving with speed of \( (40 \mathrm{~m} / \mathrm{s}) \) the driver have resorted to the use of brakes to reduce the speed of the train movement by rate \( \left(-2 \mathrm{~m} / \mathrm{s}^{2}\right) \) Calculate: a) The amount of time it takes for the train even stops completely. b) The amount of distance traveled since the train began braking until it stops

Quelle est l'unité de la valeur d'une tension? Quelle est l'unité de la valeur d'une intensité ?