Tag: physics

Questions Related to physics

An electric iron draws a current of 15 A from a 220 V supply. What is the cost of using iron for 30 min everyday for 15 days if the cost of unit (1 unit $=$ 1 k W hr) is 2 rupees?

physics electric current and its effects electric fuse electrical fuse and mcb fuse

  1. Rs. 49.5

  2. Rs. 60

  3. Rs. 40

  4. Rs. 10

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Correct Option: A
Explanation:

$I=15 A, V=220 V, t=30 min$
$Energy=P\times t=VIt$
$=220\times 15\times \frac {30}{60}\times 15$
$=3300\times \frac {1}{2}\times 15 W hr$
$=3.3\times kW\times 7.5 hr$
$=24.75 kW hr$
$Cost=24.75\times 2=Rs. 49.50$

The parameter irrelevant for an electric fuse wire is 

physics electric current and its effects electric fuse electrical fuse and mcb fuse

  1. its radius.

  2. its specific resistance.

  3. current flowing through it.

  4. its length.

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Correct Option: D
Explanation:

For fuse wire expression for heat produced is given by eq. is  $H = \dfrac{I^2 \rho}{2 \pi ^2r^3}$
Hence, it is independent on length of fuse wire. Thus, the parameter irrelevant for an electric fuse wire is its length.

State whether true or false :
The hollow shaft is much stronger than a solid shaft of same mass, same length and same material.

physics mechanical properties of solids applications of elasticity elastic energy properties of matter

  1. True

  2. False

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Correct Option: A
Explanation:

Modulus of elasticity = $\dfrac { stress }{ strain } $     and, stress = $\dfrac { Force }{ Area } $

$\therefore $  Elasticity $\alpha \dfrac { 1 }{ Area } $
As follow shaft, so, elasticity of the follow shaft is more than a solid one. As elasticity measures rigidity. So, hollow shaft is stronger.

In which year Robert Hooke presented his law of elasticity?

physics mechanical properties of solids applications of elasticity elastic energy properties of matter

  1. 1672

  2. 1674

  3. 1676

  4. 1678

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Correct Option: C
Explanation:

In 1676, Robert Hooke presented his law of elasticity, now called Hooke's law.

 A cable that can support a load of 1000 N is cut into equal parts. the maximum load that can be supported by the either part is:-
physics mechanical properties of solids applications of elasticity elastic energy properties of matter

  1. 1000 N

  2. 2000 N

  3. 500 N

  4. 250 N

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Correct Option: A
Explanation:

Maximum load supported by the cable is directly proportional to the breaking stress.

Since,

Breaking stress = F / A

where F is the force and A is the cross-sectional area.

As we see that the breaking stress is independent of the length of the cable. So, if the cable is cut in two equal parts, the maximum load that can be supported by either parts of the cable remain the same as before.

State whether true or false :
The metal used in construction of a bridge should have high Young's modulus.

physics mechanical properties of solids applications of elasticity elastic energy properties of matter

  1. True

  2. False

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Correct Option: A
Explanation:

Young's modulus measures modulus of elasticity of a material. 

Elasticity defines rigidity of the material. 
So, for construction, we need metals which have high elasticity i.e. high young's modulus.

A silver wire of length $10 $ metre and cross-sectional area $10^{-8} m^{2}$ is suspended vertically and a weight of $10 N$ is attached to it. Young's modulus of silver and its resistivity are $7 \times 10^{10} N/m^{2}$ and $1.59 \times 10^{8} N/m^{2}$ \Omega - m$ respectively. The increase in its resistance is equal to:-

physics mechanical properties of solids applications of elasticity elastic energy properties of matter

  1. $0.0455 \Omega$

  2. $0.455 \Omega$

  3. $0.91 \Omega$

  4. $0.091 \Omega$

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Correct Option: C

A steel wire is stretched by 5 kg wt, If the radius of the wire is doubled its Young's modulus

physics mechanical properties of solids applications of elasticity elastic energy properties of matter

  1. Remains unchanged

  2. Becomes double

  3. Becomes half

  4. Becomes 1/4 times

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Correct Option: A

In the system shown in figure pulley is smooth. String is massless and inextensible. The acceleration of the system a, tensions ${T} _{1}\ and {T} _{1}\left (g=10{m/s}^{2}\right)$ are 

physics mechanical properties of solids applications of elasticity elastic energy properties of matter

  1. $\dfrac { 20 }{ 3 } { m/s }^{ 2 },\dfrac { 50 }{ 3 } N,\dfrac { 60 }{ 3 } N$

  2. $\dfrac { 10 }{ 3 } { m/s }^{ 2 },\dfrac { 100 }{ 3 } N,\dfrac { 60 }{ 3 } N$

  3. $\dfrac { 20 }{ 3 } { m/s }^{ 2 },\dfrac { 100 }{ 3 } N,\dfrac { 60 }{ 3 } N$

  4. $\dfrac { 20 }{ 3 } { m/s }^{ 2 },\dfrac { 100 }{ 3 } N,\dfrac { 50 }{ 3 } N$

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Correct Option: C

A stone of mass 'm' s projected from a rubber catapult of length 'l' and cross-sectional area A stretched by an amount 'e'. If Y be the young's modulus of rubber then the velocity of projection of stone?

physics mechanical properties of solids applications of elasticity elastic energy properties of matter

  1. $Y \sqrt {\dfrac{Ae^2}{lm}}$

  2. $ \sqrt {\dfrac{Ae^2}{lm}}$

  3. $Y \sqrt {\dfrac{YAe^2}{lm}}$

  4. $Y \sqrt {\dfrac{YAe^4}{lm}}$

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Correct Option: C