Energy

Q. A refrigerator consumes an average $35\text{W}$ power to operate between temperature $-{10}^{\circ }\text{C}$ to ${25}^{\circ }\text{C}$. If there is no loss of energy, then how much average heat per second does it transfer ?

1. $350\text{J/s}$
2. $298\text{J/s}$
3. $263\text{J/s}$
4. $35\text{J/s}$

Q. A block is thrown upwards with a kinetic energy of $1\text{J}$. It goes up to a maximum height of $1\text{m}$. Find the mass of the block.
$[g=10{\text{m/s}}^2]$

1. $10\text{g}$
2. $100\text{g}$
3. $10\text{kg}$
4. $100\text{kg}$

Q. In a practical unit if the unit of mass becomes double and that of unit of time becomes half then 8 joules will be equal to ______ unit of work Options: 6 4 1 10

Q. The area of cross-section of a railway track is $0.01{\text{m}}^2$ . The temperature variation is $10{}^{\circ }\text{C}$. Coefficient of linear expansion of material of track is ${10}^{-5}{/}^{\circ }\text{C}$. The energy stored per meter in the track is ${\text{Jm}}^{-1}$. (Young's modulus of material of track is ${10}^{11}{\text{Nm}}^{-2})$

Q. The room heater can provide only ${16}^{\circ }\text{C}$ in the room when the temperature outside is $-{20}^{\circ }\text{C}$. It is not warm and comfortable, that is why the electric stove with power of $1\text{kW}$ is also plugged in. Together these two devices maintain the room temperature of ${22}^{\circ }\text{C}$. The thermal power of the heater (in kW) is

Q. In a $L-R$ decay circuit, the initial current at $t=0$ is $I$. The total charge that has flown through the resistor till the energy in the inductor has reduced to one-fourth of its initial value is

1. $\frac{LI}{R}$
2. $\frac{LI}{2R}$
3. $\frac{LI}{\sqrt{2}R}$
4. $\frac{\sqrt{2}LI}{R}$

Q. A charged particle of mass m= 2 kg and charge 1 μ C is thrown from a horizontal ground at an angle of 45^° with horizontal with a speed of 10m/s.In space a horizontal electric field E=2×10^7 N/C exists. Find the range of the projectil

Q. A solar collector receiving solar radiation at the rate of $0.6{\text{kWm}}^{-2}$ transforms it into the internal energy of a fluid at an overall efficiency of $50\%$. The fluid heated to $350\text{K}$ is used to run a heat engine which rejects heat at $313\text{K}$. If the heat engine is to deliver $2.5\text{kW}$ power, the minimum area of the solar collector required would be

1. $83.33{\text{m}}^2$
2. $16.66{\text{m}}^2$
3. $39.68{\text{m}}^2$
4. $79.36{\text{m}}^2$

Q. An object of mass $50\text{kg}$ is raised to a height of $10\text{m}$ above the ground. If the object is allowed to free fall. What is kinetic energy, when it is half way down? ($g=10{\text{m/s}}^2$)

1. $1250\text{J}$
2. $2500\text{J}$
3. $3750\text{J}$
4. $5000\text{J}$

Q. two particles revolving in circular paths under mutual gravitational force. If ratio of their kinetic energy is 1:8, then what is the ratio of their masses?

Q. A $2\text{g}$ bullet moving with a speed of $210\text{m/s}$ brought to a sudden stoppage by an obstacle. The total heat produced goes to the bullet. If the specific heat of the bullet is $0.03{\text{cal/g}}^{\circ }\text{C}$ the rise in its temperature will be

1. ${175}^{\circ }\text{C}$
2. ${180}^{\circ }\text{C}$
3. ${150}^{\circ }\text{C}$
4. ${125}^{\circ }\text{C}$

Q. 71.A charged particle of mass m and charge q is projected from large distance towards another identical charge with speed v. Potential energy of system at minimum separation

Q. A rod is fixed between two points at ${20}^{\circ }$. The coefficient of linear expansion of material of rod is $\frac{1.1\times {10}^{-5}}{{}^{\circ }C}$ and Young's modulus is $1.2\times {10}^{11}\frac{N}{m^2}$. Find the stress developed in the rod if temperature of rod becomes ${10}^{\circ }C$

1. 
2. 
3. 
4. 

Q. Figure shows the graph of elastic potential energy $\left(U\right)$ stored versus extension, for a steel wire $(Y=2\times {10}^{11}\text{Pa})$ of volume $200\text{cc}$. If area of cross-section $\left(A\right)$ and original length $\left(L\right)$, then

1. $A={10}^{-4}{\text{m}}^2$
2. $A={10}^{-3}{\text{m}}^2$
3. $L=1.5\text{m}$
4. $L=2\text{m}$

Q. 23. Derive the equation for energy lost in a capacitor

Q. Two different masses are dropped from same heights, then just before these strike the ground, the following is same

1. Kinetic energy
2. Potential energy
3. Linear momentum
4. Acceleration

Q. Two similar balloons filled with helium gas are tied to $Lm$ long strings. A body of mass m is tied to another ends of the strings. The balloons float on air at distance r. If the amount of charge on the balloons is same then the magnitude of charge on each balloon will be

1. ${\left[\frac{mgr}{2k}\cot \theta \right]}^{1/2}$
2. ${\left[\frac{2k}{mg{r}^2}\tan \theta \right]}^{1/2}$
3. ${\left[\frac{mg{r}^2}{2k}\tan \theta \right]}^{1/2}$
   
   
4. ${\left[\frac{2k}{mgr}\tan \theta \right]}^{1/2}$

Q. A man weighing 49kg carries a bag of 2 kg. He climbs to the top of a building 100m tall in 5 minutes. Calculate the work done by the man and the power he develops.

Q. An ideal massless spring $S$ can be compressed by $1m$ by a force of $100N$ in equilibrium. The same spring is placed at the bottom of a frictionless inclined plane at ${30}^{\circ }$ to the horizontal. A $10kg$ block $M$ is released from rest at the top of the incline and is brought to rest momentarily after compressing the spring by $2m$. If $g=10m/s^2$, what is the speed of mass just before it touches the spring?

1. $\sqrt{20}m/s$
2. $\sqrt{30}m/s$
3. $\sqrt{10}m/s$
4. $\sqrt{40}m/s$

Q. A metal block of heat capcity $80\text{J}{/}^{\circ }\text{C}$ placed in a room at ${20}^{\circ }\text{C}$ is heated electrically. The heater is switched off when the temperature reaches ${30}^{\circ }\text{C}$. The temperature of the block rises at the rate of $2^{\circ }\text{C/s}$ when the heater is switched on and falls at the rate of ${0.2}^{\circ }\text{C/s}$ just after the heater is switched off. Assume Newton's law of cooling to be applicable. If the power radiated at ${25}^{\circ }\text{C}$ represents the average value in the heating process, the time for which the heater was kept on is:

1. $3.3\text{sec}$
2. $4.3\text{sec}$
3. $5.3\text{sec}$
4. $6.3\text{sec}$

Q. Satellite power requirements are mainly provided through

1. Solar cells
2. Dry cells
3. Nickel cadmium cells
4. Lead - acid batteries

Q. A uniform metal rod of $4{\text{mm}}^2$ cross-section is heated from $0^{\circ }\text{C}$ to ${40}^{\circ }\text{C}$. The coefficient of linear expansion of the rod is $2\times {10}^{-6}/{}^{\circ }\text{C},Y={10}^{11}{\text{N/m}}^2$. The energy stored per unit volume of the rod is

1. $320{\text{J/m}}^3$
2. $1440{\text{J/m}}^3$
3. $2880{\text{J/m}}^3$
4. $5760{\text{J/m}}^3$.

Q. A bullet of mass $10\times {10}^{-3}\text{kg}$ moving with a speed of $20m{s}^{-1}$ hits an ice block $\left(0^{\circ }\text{C}\right)$ of mass $990\text{g}$ kept at rest on a frictionless floor and gets embedded in it. If ice takes $50\%$ of K.E lost by the system, the amount of ice melted (in $\text{grams}$) approximately is
(Latent heat of ice $=80\text{cal/g}$)

1. $6$
2. $3$
3. $6\times {10}^{-3}$
4. $3\times {10}^{-3}$

Q. Two unequal masses are tied together with a cord with a compressed spring in between.
Which one is correct ?

1. None of above answer is correct
2. Both mases will have equal KE.
3. Lighter block will have greater KE.
4. Heavier block will have greater KE.

Q. How many joules is equal to one calorie?

1. 4
2. 4.2
3. 4.4
4. 4.6

Q. if the unit of force is 1 Newton and the unit of work done is 10 joules and the unit of time is one second the unit of mass is

Q. A wind - powered generator converts wind energy into electrical energy. Assume that the generator converts a fixed fraction of the wind energy intercepted by its blades into electrical energy. For wind speed V, the electrical power output will be proportional to

1. $V^3$
2. $V^4$
3. $V$
4. $V^2$

Q. A wooden cube just floats inside water with a $200gm$ mass placed on it. When the mass is removed, the cube floats with its top surface $2cm$ above the water level. What is the side of the cube?

1. $6cm$
2. $8cm$
3. $10cm$
4. $12cm$

Q. Under the action of a force, a $2\text{kg}$ body moves such that its position $x$ as a function of time t is given by $x=\frac{t^3}{3}$, where $x$ is in meter and $t$ in second. The work done by the force in the first two seconds is

1. $1600\text{J}$
2. $1.6\text{J}$
3. $160\text{J}$
4. $16\text{J}$

Q. Capacitor of capacitance 20 HF is charged to apotential of 500 V, connected in parallel withanother uncharged capacitor of capacitarnce30 uF. The energy loss in redistribution ofcharge isE(1) 2.5J(2) 1 J(3) 0J(4)1.5 J