11.

State the energy changes in the following devices while in use:

i) A loud speaker

ii) A glowing electric bulb

A man having a box on his head, climbs up a slope and another man having an identical box walks the same distance on a levelled road.? What does more work against the force of gravity and why? 

A body is thrown vertically upwards. Its velocity keeps on decreasing. What happens to its kinetic energy as its velocity becomes zero. 

What is the principle of an ideal machine? 

Two forces each of 5 N act vertically upwards and downwards respectively on the the two ends of a uniform metre rule which is placed at its mid-point as shown in the diagram. Determine the magnitude of the resultant moment of these forces about the mid-point? 

Draw a diagram to show how a single pulley can be used so as to have its ideal M.A. = 2

Derive a relationship between mechanical advantages, velocity ratio and efficiency of a machine. 

Draw the diagram given below and clearly show the path taken by the emergent ray. 

A ray of light from water to air. How does the speed of light change? 

Name the factors affecting the critical angle for the pair of media.