Question

Two wires of equal lengths are made of the same material. Wire $$A$$ has a diameter that is twice as that of wire $$B.$$ If identical weights are suspended from the ends of these wires, the increase in length is

A. four times for wire $$A$$ as for wire $$B$$
B. twice for wire $$A$$ as for wire $$B$$
C. half for wire $$A$$ as for wire $$B$$
D. one-fourth for wire $$A$$ as for wire $$B$$  
Answer :   one-fourth for wire $$A$$ as for wire $$B$$
Solution :
$$\eqalign{ & l = \frac{{FL}}{{AY}} \Rightarrow l \propto \frac{1}{{{r^2}}}\,\,\left( {F,\;L\,{\text{and}}\,Y\,{\text{are}}\,{\text{same}}} \right) \cr & \frac{{{l_A}}}{{{l_B}}} = {\left( {\frac{{{r_B}}}{{{r_A}}}} \right)^2} = {\left( {\frac{{{r_B}}}{{2{r_B}}}} \right)^2} = \frac{1}{4} \Rightarrow {l_A} = 4{l_B} \cr & {\text{or}}\,\,{l_B} = \frac{{{l_A}}}{4} \cr} $$

Releted MCQ Question on
Basic Physics >> Mechanical Properties of Solids and Fluids

Releted Question 1

The following four wires are made of the same material. Which of these will have the largest extension when the same tension is applied?

A. $$length=50\,cm, \,\,diameter=0.5 \,mm$$
B. $$length = 100 \,cm, \,\,diameter= 1 \,mm$$
C. $$length= 200 \,cm, \,\,diameter= 2 \,mm$$
D. $$length=300 \,cm, \,\,diameter =3 \,mm$$
Releted Question 2

A U-tube of uniform cross section (see figure) is partially filled with a liquid I. Another liquid II which does not mix with liquid I is poured into one side. It is found that the liquid levels of the two sides of the tube are the same, while the level of liquid I has risen by $$2 \,cm.$$  If the specific gravity of liquid I is $$1.1,$$  the specific gravity of liquid II must be-
Mechanical Properties of Solids and Fluids mcq question image

A. $$1.12$$
B. $$1.1$$
C. $$1.05$$
D. $$1.0$$
Releted Question 3

A homogeneous solid cylinder of length $$L\left( {L < \frac{H}{2}} \right),$$   cross-sectional area $$\frac{A}{5}$$ is immersed such that it floats with its axis vertical at the liquid-liquid interface with length $$\frac{L}{4}$$ in the denser liquid as shown in the figure. The lower density liquid is open to atmosphere having pressure $${P_0}.$$ Then density $$D$$ of solid is given by-
Mechanical Properties of Solids and Fluids mcq question image

A. $$\frac{5}{4}d$$
B. $$\frac{4}{5}d$$
C. $$4d$$
D. $$\frac{d}{5}$$
Releted Question 4

A large open tank has two holes in the wall. One is a square hole of side $$L$$ at a depth $$y$$ from the top and the other is a circular hole of radius $$R$$ at a depth $$4y$$  from the top. When the tank is completely filled with water, the quantities of water flowing out per second from both holes are the same. Then, $$R$$ is equal to-

A. $$\frac{L}{{\sqrt {2\pi } }}$$
B. $$2\pi L$$
C. $$L$$
D. $$\frac{L}{{2\pi }}$$

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