Disintegration rate of a sample is `10^10` per hour at 20 hrs from the start. It reduces to` 6.3 xx 10^9 `per hour after 30 hours. Calculate its half life andthe initial number ofradioactive atoms in the sample.

The rate constant of a first order reaction is 3 xx 10^(-6) per second. If the initial concentration is 0.10 M , the initial rate of reaction is

If T.V.of rating 10 W is operated for 6 hr per day,find the number of units consumed in a leap year.

The mass of an electron is 9.1 xx 10^-31 kg. If its K.E is 3.0 xx 10^-25 J . Calculate its wavelength.

An electric bulb rated 60 w is used 10 hours per day for 20 days. If the cost of a unit is Rs 3.00 find the energy bill.

A sample of .^32P initially shows activity of one curle.After 303 days the activity falls to 1.5 xx 10^(4) dps.What is the half life of .^32P ?

Places A and B are 30 km apart and they are on a straight road.Hamid travels from A to B on bike. At the same time Joseph starts from B on bike and travels towards A. They meet each other after 20 minutes. If Joseph would have started from B at the same time but in the opposite direction (instead of towards A), Hamid would have caught up with him after 3 hours. Find the speed of Hamid and Joseph.

A metal rod 1/ sqrt(pi) meter long rotates about one of its ends in a plane perpendicular to a uniform magnetic induction 5 xx 10^-3 (Wb)/m^2 . Calculate the number of revolutions the rod makes per minute if the induced e.m.f. across it is 15 millivolt.