Questions Related to physics

Multiple choice forces on solids elastic and plastic substances forces and matter properties of matter physics

A steel rod of length $5\ m$ is fixed rigidly between two supports, $\alpha$ of steel$=12\times 10^{-6}/^{o}\ C$, $Y=2\times10^{12}Nm^{-2}$. With the increase in its temperature by $40^{o}\ C$, the stress developed in the rod is

  1. $9.6\times10^{5}\ Nm^{-2}$

  2. $9.6\times10^{6}\ Nm^{-2}$

  3. $9.6\times10^{7}\ Nm^{-2}$

  4. $9.6\times10^{8}\ Nm^{-2}$

Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice forces on solids elastic and plastic substances forces and matter properties of matter physics

A bar of cross-section A is subjected to equal and opposite tensile forces at its ends. Consider a plane section of the bar whose normal makes an angle $\theta$ with the axis of the bar.
For what value of $\theta$ is the tensile stress maximum?

  1. 0

  2. 1

  3. cant say

  4. 90

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Tensile stress$=\cfrac { force }{ area } =\cfrac { F\cos { \theta  }  }{ A\sec { \theta  }  } $
$=\cfrac { F }{ A } \cos ^{ 2 }{ \theta  } $
Tensile strength will be maximum when $\cos ^{ 2 }{ \theta  } $ is maximum i.e., $\cos { \theta  } =1$ or $\theta =0°$
Multiple choice forces on solids elastic and plastic substances forces and matter properties of matter physics

A composite rod is 1000 mm long, its two ends are 40 $mm^2$ and 30 $mm^2$ in area and length are 300 mm and 200 mm respectively. The middle portion of the rod is 20 $mm^2$ in area and 500 mm long. If the rod is subjected to an axial tensile load of 1000 N, find its total elongation (in mm). (E = 200 GPa).

  1. 0.165

  2. 0.111

  3. 0.196

  4. none of the above

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

$k=\dfrac{EA}{L}$

$k _1=\dfrac{EA _1}{L _1}$,$k _2=\dfrac{EA _2}{L _2}$,$k _3=\dfrac{EA _3}{L _3}$
$k _1=E\times \dfrac{40}{300} \times 10^{-3}$
$k _2=E\times \dfrac{30}{200} \times 10^{-3}$
$k _3=E\times \dfrac{20}{500} \times 10^{-3}$
$k _1=\dfrac{4E}{3} \times 10^{-4}$
$k _1=\dfrac{3E}{3} \times 10^{-4}$
$k _1=\dfrac{2E}{3} \times 10^{-4}$
$k _1,k _2,k _3$ are in series.
$\dfrac{1}{k _{eq}}=\dfrac{1}{k _1}+\dfrac{1}{k _2}+\dfrac{1}{k _3}$
$=\dfrac{3\times 10^4}{4E}$+$\dfrac{2\times 10^4}{3E}$+$\dfrac{5\times 10^4}{2E}$
$=\dfrac{10^4}{E}(\dfrac{3}{4}+\dfrac{2}{3}+\dfrac{5}{2})$
$=\dfrac{10^4}{E} \times \dfrac{47}{12}$
$k _{eq}=\dfrac{12E}{47} \times 10^{-4}$
$F=1000N$
$1000=\dfrac{12E}{47}\times 10^{-4} \Delta l$
$\Delta l=\dfrac{1000 \times 47}{12E}\times 10^4$
$\Delta l=\dfrac{1000\times 47 \times 10^4}{12\times 200 \times 10^9}$
$=19.6\times 10^{-5}$
$=0.196 mm$

Multiple choice forces on solids elastic and plastic substances forces and matter properties of matter physics

A steel wire AB of length 100 cm is fixed rigidly at points A and B in an aluminium frame as shown in the figure If the temperature of the system increases through 100C, then the excess stress produced in the steel wire relative to the aluminium? ${ \alpha } _{ \mu }=22\times { 10 }^{ -6 }{ / }^{ 0 }Cand{ \alpha } _{ stret }=11\times { 10 }^{ -6 }{ / }^{ 0 }C$ young 's modulus of steel is $2\times { 10 }^{ 31 }{ Nm }^{ -2 }$

  1. $2.2\times { 10 }^{ 5 }$Pa

  2. $22\times { 10 }^{ 2 }$Pa

  3. $2.2\times { 10 }^{ 2 }$Pa

  4. $220\times { 10 }^{ 2 }$Pa

Reveal answer Fill a bubble to check yourself
C Correct answer
Multiple choice forces on solids elastic and plastic substances forces and matter properties of matter physics

A steel rod of length $1m$ and radius $10mm$ is stretched by a force $100kN$ along its length. The stress produced in the rod is then
 $\left( { Y } _{ steel }=2\times { 10 }^{ 11 }N\quad { m }^{ -2 } \right) $

  1. $3.18\times { 10 }^{ 6 }N\quad { m }^{ -2 }$

  2. $3.18\times { 10 }^{ 7 }N\quad { m }^{ -2 }\quad $

  3. $3.18\times { 10 }^{ 8 }N\quad { m }^{ -2 }$

  4. $3.18\times { 10 }^{ 9 }N\quad { m }^{ -2 }\quad $

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Here $r=10mm=10\times { 10 }^{ -3 }m={ 10 }^{ -2 }m$
$L=1m,F=100kN=100\times { 10 }^{ 3 }N={ 10 }^{ 5 }N$

Stress produced in the rod is:
$Stress=\cfrac { F }{ A } =\cfrac { F }{ \pi { r }^{ 2 } } =\cfrac { 100\times { 10 }^{ 3 }N }{ 3.14\times { \left( { 10 }^{ -2 }m \right)  }^{ 2 } } =3.18\times { 10 }^{ 8 }N\quad { m }^{ -2 }\quad $

Multiple choice forces on solids elastic and plastic substances forces and matter properties of matter physics

One end of a uniform wire of length L and of weight W is attached rigidly to a point in the roof and
a weight $W _{1}$ is suspended from its lower end. If S is the are of cross-section of the wire, the stress in
the wire at a height (3 L /4) from its lower end is :

  1. $W _{1}/S$

  2. $[W _{1}+(W/4)]/S$

  3. $[W _{1}+(3W/4)]/S$

  4. $W _{1}+(W)/S$

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The stress at a point is the total force below that point divided by the area. The weight of the wire below the point at 3L/4 from the bottom is (3/4)W. The total force is W1 + (3/4)W. Stress = (W1 + 3W/4) / S.

Multiple choice physics structure of earth electricity from water energy hydro electricity hydro energy

The water stored in the dam on a river has .................. .

  1. Kinetic energy

  2. Potential energy

  3. Electrical energy

  4. Biomass energy

Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

The water stored in the dam on a river has potential energy.
The potential energy stored in a body of water held at a given height is converted to kinetic energy (movement energy) which is used to turn a turbine and create electricity.

Multiple choice physics structure of earth electricity from water energy hydro electricity hydro energy

The tidal power plants are constructed near the mouth of ................ bays.

  1. $renewable$

  2. $huge$

  3. $narrow$

  4. $broad$

Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Tidal energy of sea waves is harnessed by constructing hydro electric dams at the mouth of narrow bays along the sea coast.
Hence, The tidal power plants are constructed near the mouth of narrow bays.

Multiple choice physics structure of earth electricity from water energy hydro electricity hydro energy

The ultimate source of hydroelectric energy is :

  1. potential energy of water

  2. kinetic energy of water

  3. solar energy

  4. chemical energy

Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Answer is A.

Potential energy is the energy that is stored in an object due to its position relative to some zero position. An object possesses gravitational potential energy if it is positioned at a height above (or below) the zero height.
There is potential energy stored in a water reservoir behind a dam. It is converted to kinetic energy when the water starts flowing down the penstock, from the dam. This kinetic energy is used to turn a turbine.
Hence, the source for hydro electricity power generation is potential energy of water.