question_answer

A body weighs 500 N on the surface of the earth. How much would it weigh half way below the surface of the earth?

A)                 1000 N                 

B)                  500 N

C)                  250 N                                   

D)                  125 N

Correct Answer: C

Solution :

                Key Idea: Value of acceleration due to gravity decreases on going below the surface of the earth. Weight (w) of a body is defined as product of mass (m) and acceleration due to gravity (g) w = mg The value of g below the surface of earth at a distance h is given by                 \[={{\varepsilon }_{0}}\,\,E_{rms}^{2}\] \[=8.85\times {{10}^{-12}}\times {{(720)}^{2}}\]                \[=4.58\times {{10}^{-6}}J/{{m}^{3}}\] Given,     \[{{10}^{-10}}s\] \[f=\frac{v}{v-{{v}_{s}}}f\]           \[{{v}_{s}}\]                 \[v=320m/s,\,{{v}_{s}}=4m/s,\,f=240Hz\] Note: Value of g also decreases ongoing above the surface of earth, as follows                 \[f=\frac{320}{320-4}\times 240\]