16) A body of mass 3.14 kg is suspended form one end of a wire of length 10 m. The radius if cross - section of the wire is changing uniformly from $5\times {10}^{-4}m$ at the top (i.e. point of suspension) to $9.8\times {10}^{-4}m$at the bottom. Young's modulus of elasticity is $2\times {10}^{11}N/{m}^{2}.$ The change of length of the wire is. $\left(a\right)4\times {10}^{-3}m\phantom{\rule{0ex}{0ex}}\left(b\right)3\times {10}^{-3}m\phantom{\rule{0ex}{0ex}}\left(c\right){10}^{-3}m\phantom{\rule{0ex}{0ex}}\left(d\right)2\times {10}^{-3}m$

Q.40. In which of the following electrical devices electromagnetic motor is used?

(A) Bulb

(B) Heater

(C) Transformer

(D) Washing Machine

Solve this :$15.\mathrm{A}\mathrm{uniform}\mathrm{chain}\mathrm{of}\mathrm{lenght}\mathrm{L}\mathrm{and}\mathrm{mass}\mathrm{M}\mathrm{is}\mathrm{hanging}\mathrm{from}\mathrm{ceiling}\mathrm{as}\mathrm{shown}\mathrm{in}\mathrm{figure}.\mathrm{Tension}\mathrm{in}\mathrm{the}\mathrm{chain}\mathrm{at}\mathrm{a}\mathrm{distance}\mathrm{x}=\frac{\mathrm{L}}{4}\mathrm{from}\mathrm{the}\mathrm{lower}\mathrm{end}\mathrm{is}:\phantom{\rule{0ex}{0ex}}1.\frac{\mathrm{M}\left(\mathrm{l}-\mathrm{x}\right)\mathrm{g}}{\mathrm{l}}2.\mathrm{Mg}3.\mathrm{Zero}4.\frac{\mathrm{mxg}}{\mathrm{l}}$

16) A body of mass 3.14 kg is suspended form one end of a wire of length 10 m. The radius if cross - section of the wire is changing uniformly from $5\times {10}^{-4}m$ at the top (i.e. point of suspension) to $9.8\times {10}^{-4}m$at the bottom. Young's modulus of elasticity is $2\times {10}^{11}N/{m}^{2}.$ The change of length of the wire is.

$\left(a\right)4\times {10}^{-3}m\phantom{\rule{0ex}{0ex}}\left(b\right)3\times {10}^{-3}m\phantom{\rule{0ex}{0ex}}\left(c\right){10}^{-3}m\phantom{\rule{0ex}{0ex}}\left(d\right)2\times {10}^{-3}m$

Q.10. If the work done in stretching a wire by 1 mm is 2 J, then work necessary for stretching another wire of same material but with double radius of cross-section and half of the length by 1 mm is

(a) 8 J

(b) 16 J

(c) 4 J

(d) 32 J