Group - B Physics model question solution Part - 1 [NEB] 2077/78

                    GROUP - B

1.a) The sum of linear momentum of two colliding bodies is same before and after collision if no external forces acts on them.

  

1.c) In this case, aeroplane and earth acts as two colliding bodies and the momentum of aeroplane is transferred to earth. But the velocity of earth is too negligible to notice as it have large mass. That's how law of conservation of momentum works here.

       OR

a). Hooke's law states that the restoring force produced in a body is directly proportional to the extension produced in it within elastic limit.

b). Lets suppose the curve of deforming force w.r.t. strain be curve 'A' and the curve of reforming force be curve 'B'. As area of curve gives the work done by forces, the area of curve 'A' gives the work done by deforming force and the area of curve 'B' gives the work done by reforming force. According to figure, the work done by deforming force is greater than that of reforming force. The difference between the work done by two forces is equivalent to heat produced by tyre. Thats how heat is produced on tyre.

2.a) The specific latent heat of vaporization is the amount of heat required to convert unit mass of water from liquid state to gaseous state under constant temperature.i.e 100° C.

It means that 2.26 MJ of heat is required to convert 1 kg of water from liquid state to gaseous state under constant temperature.

c) The efficiency of every machine that exist is never 100% but less than 100%. Thats why in case of kettle, its output power is less than that of expected. As power is inversely proportional to the time taken, time taken is more than that of calculated above.

3.a) Any three properties of ideal gas as per KTG are :

- The volume of gaseous molecule is negligible as compared to total volume of gas.

- The collision between molecules of gas and wall of container is elastic.

- The intermolecular force between the gaseous molecules is negligible.

 b) As ideal gas doesn't exist, he have to use something as alternate of ideal gas. He have to do two things as follow to convert real gas into ideal :

- Maintain low pressure

- Increase the temperature of gas

4.a) The change of temperature with respect to length of a body in the direction of heat flow is called temperature gradient.

 c) Moisture increases the rate of conduction in fibre glass.