How many years it would take to spend Avogadro number of rupees at the rate of 10 lakh ruoees per second?

How many minutes it would take to reduce 0.20 mol of Cu^(2+) to Cu using a current of 10A?

The two equal sides of an isosceles triangle with fixed base b are decreasing at the rate of 3 cm per second. How fast is the area decreasing when the two equal sides are equal to the base ?

A person tries to form as many different parties as he can, out of his 20 friends. Each party should consist of the same number. How many friends should be invited at a time? In how many of these parties would the same friends be found?

A radioactive source, in the form of a metallic sphere of radius 10^(-2)m emits beta -particles at the rate of 5xx10^(10) particles per second. The source is electrically insulated. How long will it take for its potential to be raised by 2V, assuming that 40% of the emitted beta -particles escape the source.

A cylindrical water tank of diameter 1.4 m and height 2.1 m is being fed by a pipe of diameter 3.5 cm through which water flows at the rate of 2 metre per second. In how many time the tank will be filled?

Estimating the following numbers should be interesting. The number tells you why our eye can never count photons, even in barely detetable light. The number of photons entering the pupil of our eye per second corresponding to the minimum intensity of white light that we humans can perceive (~10^-10 Wm^-2) . Take the area of the pupil to be about 0.4 cm^2 , and the average frequency of white light to be about 6 xx 10^14 Hz .

the ratio of the length to breadth of a lawn is 3:5.It costs Rs.3200/- to fence it at rate of Rs.2/- a metre.What would be the cost of developing the lawn at the rate of Rs.10/- per square metre.

A coil has an inductance of 1.5 xx 10^-2 H. Calculate the e.m.f. induced, when current in the coil changes at the rate 200 ampere per second.

A hemispherical tank full of water is emptied by a pipe at the rate of 3 4/7 litres per second. How much time will it take to empty half the tank, if it is 3m in diameter? (Take pi=22/7 )