(a) Write the two uses of radioactivity.

(b) A crow-bar of length 80 cm has its fulcrum situated at a distance of 10 cm from the load. Calculate the mechanical advantage of the crow-bar.

(c) Why fission nuclei undergo β-decay?

(a) Uses of radioactivity :

1. Many diseases such as leukemia, cancer, etc., are cured by radiation therapy.
2. Radioisotopes are used to trace and study the uptake of nutrients by plants. For example, the use of radioactive phosphorous ³²P in fertilizers has revealed how phosphorous is absorbed by plants.

(b) Given,

Total length of a crowbar = 80 cm

Effort arm = 80 - 10 = 70 cm

Load arm = 10 cm

We know that,

$\text{M.A.} = \dfrac{\text{Effort arm}}{\text{Load arm}} \\[0.5em] \text{M.A.}. = \dfrac{70}{10} \\[0.5em] \Rightarrow\text{M.A.} = 7 \\[0.5em]$

Hence, mechanical advantage = 7

(c) Fission reactions primarily release energy in the form of neutrons. Some of the neutrons produced during fission are initially in an excited state. Beta decay occurs when a neutron in this excited state transforms into a proton, emitting a beta particle (an electron) and an antineutrino. This process helps stabilize the nucleus by converting a neutron into a proton, maintaining a balance between protons and neutrons in the nucleus.