(a) In the following atoms, which one is a radioisotope? Give one use of this isotope.

O¹⁶, C¹⁴, N¹⁴, He⁴

(b) Name the class of the lever shown in the picture below :

Fill in the blanks :

(a) When a stone tied to a string is rotated in a horizontal plane, the tension in the string provides …………… force necessary for circular motion.

(b) Work done by this force at any instant is …………… .

Meera chose to use a block and tackle system of ‘9’ pulleys instead of a single movable pulley to lift a heavy load.

(a) What is the advantage of using a block and tackle system over a single movable pulley?

(b) Why should she connect more number of pulleys in the upper fixed block?

Sumit does 600 J of work in 10 min and Amit does 300 J of work in 20 min. Calculate the ratio of the powers delivered by them.