Properties of matter questions | form five Physics

Briefly explain the following observations

1. soap solution is a better cleansing agent than ordinary water.
2. When a piece of chalk is put into water, it emits bubbles in all directions.

Two spherical soap bubbles are combined . If V is the change in volume of the contained air, A is the change in total surface area, show that , where T is the surface tension and P_a is the atmospheric pressure.

There is a soap bubble of radius 3.6x10^-4m in air cylinder which is originally at a pressure of 10⁵Nm². The air in the cylinder is now compressed isothermally until the radius of the bubble is halved. Calculate the pressure of air in the cylinder.

1. What is strain energy?
2. A piece of rod 1.05m long whose weight is negligible is supported at its ends by wires Q and P of equal lengths as shown in figure 1.

The cross sectional area of P is 1mm² and that of Q is 2mm². At what point along the bar should the weight be suspended in order to produce

1. Equal stress of P and Q
2. Equal strain of P and Q

(Given Young`s modulus of wire P=2.4x10¹¹Nm^-2 and that of wire Q=1.6x10¹¹Nm^-2)

Define the following materials as classified on the basis of elastic properties

1. Ductile materials
2. Brittle materials
3. Elastomers

Briefly explain why the stretching of a coil spring is determined by its shear modulus.

A copper wire of negligible mass , 1m long and cross-sectional area 10^-5m² is kept on a smooth horizontal table with one end fixed. A ball of 1kg is attached to the other end. The wire and the ball are rotating with an angular velocity of 35rad/s. If the elongation of the wire is 10^-2m, find Young`s modulus of wire. If on increasing the angular velocity to 100rad/s, the wire breaks down, find the breaking stress.

Differentiate bulk modulus from shear modulus.

Two wires , one of steel and one of phosphor bronze each 1.5m long and 2mm diameter are joined end to end as a composite wire of length 3cm. What tension in the composite wire will produce total extension of 0.064cm?.

Define the term proportional limit,elastic limit,yield point and elasticity.