1,168 practice questions for CBSE Class 11 Physics, organised by NCERT chapter (14 chapters). Every question includes a written explanation. Pick a chapter below, or try the samples first.
A particle of mass $0.2\ \text{kg}$ moves along the $x$-axis under a net force $F = -8x$, where $F$ is in newtons and $x$ is the displacement from the origin in metres. Consider these statements. (I) The motion is simple harmonic about $x = 0$. (II) The angular frequency is $\sqrt{40}\ \text{rad/s}$. (III) The acceleration of the particle at $x = 0.5\ \text{m}$ is $-4\ \text{m/s}^2$. Which statements are correct?
AII and III only
BI and III only
CI and II only
DI, II and III
Show answer and explanation
Correct answer: C - I and II only
A restoring force proportional to displacement and directed towards $x = 0$ is exactly the condition for SHM, so (I) is correct. Here $k = 8\ \text{N/m}$, giving $\omega = \sqrt{k/m} = \sqrt{8/0.2} = \sqrt{40}\ \text{rad/s}$, so (II) is correct. At $x = 0.5\ \text{m}$ the force is $-4\ \text{N}$ and the acceleration is $F/m = -4/0.2 = -20\ \text{m/s}^2$, so (III) mistakes the force for the acceleration.
Q2
medium
A car radiator uses water as a coolant. Why is water preferred over other liquids?
AWater has a high specific heat capacity.
BWater is a good conductor of electricity.
CWater is a dense liquid, providing better flow.
DWater has a low boiling point.
Show answer and explanation
Correct answer: A - Water has a high specific heat capacity.
Water is preferred because its high specific heat capacity allows it to absorb more heat without a large temperature rise, making it an efficient coolant. It is not chosen for electrical conductivity, boiling point, or density, which don't enhance cooling.
Q3
medium
Assertion (A): At the highest point of a vertical throw both the velocity and the acceleration of the body are zero.
Reason (R): Gravity acts on the body throughout its flight, giving it a constant downward acceleration of about $9.8\,\mathrm{m\,s^{-2}}$.
ABoth A and R true, R explains A
BBoth A and R true, R does not explain A
CA true, R false
DA false, R true
Show answer and explanation
Correct answer: D - A false, R true
A is false. The velocity is indeed zero for an instant at the top, but the acceleration is not: were it zero, the body would simply stay up there instead of coming down. R is true, and it shows why the acceleration remains $9.8\,\mathrm{m\,s^{-2}}$ downwards even at the instant when the velocity passes through zero.
Q4
easy
Bernoulli's equation, $P + \frac{1}{2}\rho v^2 + \rho g h = \text{constant}$ along a streamline, is a statement of which conservation law applied to a flowing fluid?
AConservation of mass
BConservation of angular momentum
CConservation of energy
DConservation of linear momentum
Show answer and explanation
Correct answer: C - Conservation of energy
Each term is an energy per unit volume: pressure energy, kinetic energy and potential energy. Their sum staying constant along a streamline is conservation of energy for the moving fluid. Conservation of mass is expressed separately by the equation of continuity $A_1v_1 = A_2v_2$, and neither momentum equation takes this form.
Q5
medium
Steel rivets are heated until they glow before being hammered through matching holes in two steel plates. Why does the joint become extremely tight once the rivet has cooled?
AThe rivet contracts as it cools and pulls the two plates firmly together
BThe rivet expands as it cools and presses outwards against the walls of the hole
CThe plates contract on cooling far more than the rivet does and squeeze it flat
DThe rivet loses its elasticity on cooling and simply hardens inside the hole
Show answer and explanation
Correct answer: A - The rivet contracts as it cools and pulls the two plates firmly together
A hot rivet is slightly longer than it will be when cold, so as it cools it contracts and draws the two plate faces together, clamping them under a large force. Metals contract rather than expand when they cool, so the idea that the rivet expands as it cools reverses the rule. The plates are the same metal and cool along with the rivet, so they cannot out-contract it, and hardening on its own supplies no clamping force.
Q6
medium
The angular momentum of a wheel falls uniformly from $30\ \text{kg m}^2\text{/s}$ to $6\ \text{kg m}^2\text{/s}$ in $8\ \text{s}$. What is the magnitude of the average external torque acting on it?
A$0.75\ \text{N m}$
B$3\ \text{N m}$
C$4.5\ \text{N m}$
D$24\ \text{N m}$
Show answer and explanation
Correct answer: B - $3\ \text{N m}$
Since $\tau = \Delta L/\Delta t$, the torque is $(30 - 6)/8 = 3\ \text{N m}$. The value $24\ \text{N m}$ quotes the change in angular momentum itself without dividing by the time, $4.5\ \text{N m}$ adds the two angular momenta instead of subtracting them, and $0.75\ \text{N m}$ uses only the final value.
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