What sort of arrangement is to be taken so that an object will not be visible even in the presence of light?

At what distance in front of a concave mirror (f = 10m) an object is to be placed so that the size of the image will be halved of the size of the object?

What sort of a reflector is used with a street bulb to light up streets in a better way ?

What will form aspirin on heating to about 55^@C with acetic anhydride in the presence of little conc. H_2SO_4 ? Write the structure of aspirin.

A loaded lorry of total mass 5000 kg can come down from the top of a slope (1:40) effortlessly at 18 km *h^(-1) . What should be the horsepower of its engine so that it can go up with the same speed, from the base to the top ? Resistance due to friction may be taken to be the same in both cases.

Whats is the probability of arrangement of the letters of the word SOCIETY so that three vowels come together?.

At what distance an object to be kept from a convex lens so that its image will be equal in size?