Two exactly similar wires of steel and copper are stretched by equal forces. If the total elongation is 2 cm, then how much is the elongation in steel and copper wire respectively? Given, ${\mathrm{Y}}_{\mathrm{steel}}=20\times {10}^{11} \mathrm{dyne}/{\mathrm{cm}}^2, {\mathrm{Y}}_{\mathrm{copper}}=12\times {10}^{11} \mathrm{dyne}/{\mathrm{cm}}^2.$

1. 1.25 cm; 0.75 cm

2. 0.75 cm; 1.25 cm

3. 1.15 cm; 0.85 cm

4. 0.85 cm; 1.15 cm

The proportional limit of steel is $8\times {10}^8 \mathrm{N}/{\mathrm{m}}^2$ and its Young's Modulus is $2\times {10}^{11} \mathrm{N}/{\mathrm{m}}^2$. The maximum elongation, a one metre long steel wire can be given without exceeding the proportional limit is

1. 2 mm

2. 4 mm

3. 1 mm

4. 8 mm

In a series combination of copper and steel wires of same length and same diameter, a force is applied at one of their ends while the other end is kept fixed. The combined length is increased by 2 cm. The wires will have

1. Same stress and same strain

2. Different stress and different strain

3. Different stress and same strain

4. Same stress and different strain

If in case A, elongation in wire of length L is l, then for same wire, elongation in case B will be-

1. 4l

2. 2l

3. l

4. l/2

Energy stored per unit volume in a stretched wire having Young's Modulus Y and stress 'S' is

1. $\frac{\mathrm{YS}}{2}$

2. $\frac{{\mathrm{S}}^2\mathrm{Y}}{2}$

3. $\frac{{\mathrm{S}}^2}{2\mathrm{Y}}$

4. $\frac{\mathrm{S}}{2\mathrm{Y}}$

A wire suspended vertically from one end and is stretched by attaching a weight 200 N to the lower end. The weight stretches the wire by 1 mm. The elastic potential energy gained by the wire is

1. 0.1 J

2. 0.2 J

3. 0.4 J

4. 10 J

Work done by restoring force in a wire within elastic limit is -10 J. Maximum amount of heat produced in the wire is

1. 10 J

2. 20 J

3. 5 J

4. 15 J

The work done per unit volume to stretch the length of area of cross-section 2 mm² by 2% will be
$\left[\mathrm{Y}=8\times {10}^{10} \mathrm{N}/{\mathrm{m}}^2\right]$

1. 40 MJ/m³ 

2. 16 MJ/m³ 

3. 64 MJ/m³ 

4. 32 MJ/m³ 

Which one of the following statements is wrong?

On stretching some substances, why is permanent elongation caused?

1. They are perfectly elastic.

2. They are perfectly plastic.

3. More stress acts on them.

4. Their strain is infinite.