21.

A uniform half metre rule balances horizontally on a knife edge at 29 cm mark when a weight of 20 gf is suspended from one end.
(i) Draw a diagram of the arrangement
(ii) What is the weight of the half metre rule?

A boy uses a single fixed pulley to lift a load of 50 kgf to some height. Another boy uses a single movable pulley to lift the same load to the same height. Compare the effort applied by them. Give a reason to support your answer.

How does uniform circular motion differ from uniform linear motion?

Name the process used for producing electricity using nuclear energy.

A pulley system with VR = 4 is used to lift a load of 175 kgf through a vertical height of 15 m. The effort required is 50 kgf in the downward direction.
(g = 10 N kg-1) Calculate
(i) Distance moved by the effort
(ii) Work done by the effort
(iii) M.A. of the pulley system
(iv) Efficiency of the pulley system

How is the transference of heat energy by radiation prevented in a calorimeter?

Calculate the mass of ice needed to cool 150g of water contained in a calorimeter of mass 50 g at 32^oC such that the final temperature is 5^oC.
Specific heat capacity of calorimeter = 0.4J/g^oC Specific heat capacity of water = 4.2 J/g^oC Latent heat capacity of ice = 330 J/g

You have a choice of three metals A,B and C, of specific heat capacities 900 Jkg^-1oC^-1, 380 Jkg^-1oC^-1 and 460 Jkg-^1oC^-1 respectively, to make a calorimeter. Which material will you select? Justify your answer.

 Name the radiations which are absorbed by greenhouse gases in the earth’s atmosphere.

A radiation X is focused by a particular device on the bulb of a thermometer and mercury in the thermometer shows a rapid increase. Name the radiation X.