A car moving at a speed ' V ' is stopped in a certain distance when the breaks produce a deceleration ' $a$ '. If the speed of the car is ' $n v$ ', what must be the deceleration of the car to stop it in the same distance and in the same time?

A radio active element has rate of disintegration 8000 disintegrations per minute at a particular instant. After four minutes it becomes 2000 disintegrations per minute. The decay constant per minute is

The closed and open organ pipes have same length. When they are vibrating simultaneously in first overtone, they produce four beats. The length of open pipe is made half and that of the closed pipe is made two times the original. Now the number of beats produced if the two pipes are vibrating in their fundamental modes simultaneously is

In series LCR circuit R $=18 \Omega$ and impedance is $30 \Omega$. An rms voltage 210 V is applied across the circuit. The true power consumed in AC circuit is nearly