Question

A steel wire of length $$l$$ and cross section area $$A$$ is stretched by $$1\,cm$$  under a given load. When the same load is applied to another steel wire of double its length and half of its cross section area, the amount of stretching (extension) is

A. $$0.5\,cm$$
B. $$2\,cm$$
C. $$4\,cm$$  
D. $$1.5\,cm$$
Answer :   $$4\,cm$$
Solution :
Young’s modulus of elasticity is
$$\eqalign{ & Y = \frac{{\frac{F}{A}}}{{\frac{{\Delta L}}{L}}} \cr & \therefore \Delta L = \frac{{FL}}{{AY}} \cr & {\text{So,}}\,\,\Delta L \propto \frac{L}{A} \cr & \therefore \frac{{\Delta {L_2}}}{{\Delta {L_1}}} = \frac{{{L_2}}}{{{L_1}}} \times \frac{{{A_1}}}{{{A_2}}} = \frac{2}{1} \times \frac{2}{1} = 4 \cr & \Delta {L_2} = 4 \times \Delta {L_1} = 4 \times 1 = 4\,cm \cr} $$

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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