Top Physics 1000 MCQs

Top Physics MCQs

چار آپشن میں سے کسی ایک پر کلک کرنے سے جواب سرخ ہو جائے گا۔

An object placed in front of a concave mirror at a distance of X cm from the pole gives a 3 times magnified real image if it is moved to distance of X+5cm, the Magnification of the image becomes 2. The focal length of the mirror is _____?

30 cm
15 cm
20 cm
None of these

(0)

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Explanation

Step 1: Mirror formula & magnification
For concave mirror:

$\frac{1}{f} = \frac{1}{u} + \frac{1}{v}, m = - \frac{v}{u}$

Real image ⇒ $m$ negative, but magnitude given: $∣ m ∣ = 3$ and $∣ m ∣ = 2$ .

Step 2: First case
$u_{1} = X$ , $m_{1} = - 3$ ⇒ $v_{1} = - 3 X$ (since $m = - v / u$ ⇒ $- 3 = - v / X$ ⇒ $v = 3 X$ )

Step 3: Second case
$u_{2} = X + 5$ , $m_{2} = - 2$ ⇒ $v_{2} = - 2 (X + 5)$

$\frac{1}{f} = \frac{1}{X + 5} + \frac{1}{2 (X + 5)} = \frac{3}{2 (X + 5)} (2)$

Step 4: Equate (1) and (2)

$\frac{4}{3 X} = \frac{3}{2 (X + 5)}$ $8 (X + 5) = 9 X$ $8 X + 40 = 9 X$ $X = 40 cm$

Step 5: Find $f$
From (1):

$\frac{1}{f} = \frac{4}{3 \times 40} = \frac{4}{120} = \frac{1}{30}$ $f = 30 cm$

When a spring is stretched by 10 cm, the potential energy is stored is E. when the spring is stretched by 10cm more, the potential energy stored in the spring becomes?

10E
2E
4E
None of these

(0)

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Explanation

Step 1: Spring potential energy formula
Potential energy stored in a spring stretched by $x$ is:

$U = \frac{1}{2} k x^{2}$

where $k$ is the spring constant.

Step 2: First case
Stretched by $x_{1} = 10 cm$ :

$E = \frac{1}{2} k (10)^{2} = 50 k$

Step 3: Second case
Stretched by $x_{2} = 10 + 10 = 20 cm$ :

$U_{2} = \frac{1}{2} k (20)^{2} = \frac{1}{2} k (400) = 200 k$

Step 4: Compare with E
From $E = 50 k$ , we have $k = E / 50$ .
But easier:

$\frac{U_{2}}{E} = \frac{200 k}{50 k} = 4$

So $U_{2} = 4 E$ .

A bullet on penetrating 30cm into its target A loses its velocity by 50%. What additional distance will its penetrate into the target before it comes to rest?

10 cm
30 cm
20 cm
None of these

(0)

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Explanation

Step 1: Relation between velocity and penetration depth
Assume the bullet experiences a constant deceleration $a$ .
From kinematics:

$v^{2} = u^{2} - 2 a s$

Let initial velocity = $u$ .

Step 2: First penetration
Penetrates $s_{1} = 30 cm$ , velocity becomes $u / 2$ :

${(\frac{u}{2})}^{2} = u^{2} - 2 a (30)$ $\frac{u^{2}}{4} = u^{2} - 60 a$ $60 a = u^{2} - \frac{u^{2}}{4} = \frac{3 u^{2}}{4}$ $a = \frac{u^{2}}{80}$

Step 2: First penetration
Penetrates $s_{1} = 30 cm$ , velocity becomes $u / 2$ :

${(\frac{u}{2})}^{2} = u^{2} - 2 a (30)$ $\frac{u^{2}}{4} = u^{2} - 60 a$ $60 a = u^{2} - \frac{u^{2}}{4} = \frac{3 u^{2}}{4}$ $a = \frac{u^{2}}{80}$

Step 3: Additional penetration to stop
From velocity $u / 2$ to 0, distance $s_{2}$ :

$0^{2} = {(\frac{u}{2})}^{2} - 2 a s_{2}$ $0 = \frac{u^{2}}{4} - 2 \cdot \frac{u^{2}}{80} \cdot s_{2}$ $\frac{u^{2}}{4} = \frac{u^{2}}{40} s_{2}$ $s_{2} = 10 cm$

Let L be the length and d be the diameter of B cross section of a wire. Wires of the same material with different L and d are subjected to the same tension along the length of the wire. In which of the following cases the extension of wire will be the maximum?

L=300 cm, d=1.0 mm
L=200cm, d=0.5 mm
L=50 cm, d=0.05 mm
L=100cm, d=0.2 mm

(0)

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Explanation

Step 1: Extension formula
Extension in a wire under tension $F$ is given by:

$Δ L = \frac{F L}{A Y}$

where $A = \frac{π d^{2}}{4}$ is cross-sectional area, $Y$ is Young’s modulus (same for same material), $F$ is same for all wires.

So:

$Δ L \propto \frac{L}{A} \propto \frac{L}{d^{2}}$

Step 2: Compute $L / d^{2}$ for each

(a) $L = 200 cm, d = 0.5 mm = 0.05 cm$

$\frac{L}{d^{2}} = \frac{200}{(0.05)^{2}} = \frac{200}{0.0025} = 80000$

(b) $L = 300 cm, d = 1.0 mm = 0.1 cm$

$\frac{L}{d^{2}} = \frac{300}{(0.1)^{2}} = \frac{300}{0.01} = 30000$

(c) $L = 50 cm, d = 0.05 mm = 0.005 cm$

$\frac{L}{d^{2}} = \frac{50}{(0.005)^{2}} = \frac{50}{0.000025} = 2,000,000$

(d) $L = 100 cm, d = 0.2 mm = 0.02 cm$

$\frac{L}{d^{2}} = \frac{100}{(0.02)^{2}} = \frac{100}{0.0004} = 250000$

The point at which an applied force A produces linear motion but no rotatory motion is _____?

Optical center
Mid-pint
Center of gravity
None of these

(0)

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Average distance of the earth from the sun A is L1. If one year of the earth =D days one year of another planet whose average distance from the sun is L2 will be ______?

D(L2/L1) days
D(L2/L1)1/2days
D(L2/L1)3/2 days
None of these

(0)

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Explanation

Step 1: Kepler’s third law
For planets around the Sun:

$T^{2} \propto a^{3}$

where $T$ is orbital period, $a$ is average distance from Sun.

Step 2: Apply to Earth and the other planet

$\frac{T_{2}}{T_{1}} = {(\frac{L_{2}}{L_{1}})}^{3 / 2}$

Given $T_{1} = D$ days (Earth’s year), $T_{2} = ?$

$T_{2} = D {(\frac{L_{2}}{L_{1}})}^{3 / 2}$

A particle is travelling among a straight line OX. The distance x in meters of the particle from O at a time t is given by X = 37 + 27t t³ where t is given by X in the seconds. The distance of particles from O when it comes to rest is W3.

101m
81m
91m
None of these

(0)

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Explanation

Step 1: Interpret the equation
The given equation is:

$x = 37 + 27 t - t^{3}$

(It seems from the text “X = 37 + 27t t³” likely means $X = 37 + 27 t - t^{3}$ because otherwise it wouldn’t make physical sense for motion.)

Step 2: Find when the particle comes to rest
Velocity $v = \frac{d x}{d t} = 27 - 3 t^{2}$ .
Set $v = 0$ :

$27 - 3 t^{2} = 0$ $t^{2} = 9$ $t = 3 s (time positive)$

Step 3: Find position at $t = 3$

$x = 37 + 27 (3) - (3)^{3}$ $x = 37 + 81 - 27$ $x = 91 m$

Ultra violet light is more likely to cause a photoelectric effect than a visible light. This is because photons of ultraviolet light _____?

Have a higher energy
Have a longer wavelength
Have higher velocity
None of these

(0)

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If A = B+C and A,B,C have scalder magnitudes of 5,4,3 unit respectively then the angle between vector A and vector B is _____?

Sin-1 (3/4)
Cos-1 (3/5)
Cos-1 (4/5)
None of these

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Explanation

Step 1: Understand the vector equation
Given:

$A = B + C$

Magnitudes: $A = 5$ , $B = 4$ , $C = 3$ .

Step 2: Use the cosine rule in vector form
From $C = A - B$ ,

$C^{2} = A^{2} + B^{2} - 2 A B \cos θ$

where $θ$ is the angle between $A$ and $B$ .

Step 3: Substitute values

$3^{2} = 5^{2} + 4^{2} - 2 (5) (4) \cos θ$ $9 = 25 + 16 - 40 \cos θ$ $9 = 41 - 40 \cos θ$ $40 \cos θ = 41 - 9 = 32$ $\cos θ = \frac{32}{40} = \frac{4}{5}$ $θ = \cos^{- 1} (\frac{4}{5})$

The dimension formula of angular momentum is?

[M L T⁻²]
[M L² T⁻¹]
[M L² T⁻²]
[M L T⁻¹]

(0)

PHYSICS

An object placed in front of a concave mirror at a distance of X cm from the pole gives a 3 times magnified real image if it is moved to distance of X+5cm, the Magnification of the image becomes 2. The focal length of the mirror is _____?

اس سوال کو وضاحت کے ساتھ پڑھیں

Explanation

When a spring is stretched by 10 cm, the potential energy is stored is E. when the spring is stretched by 10cm more, the potential energy stored in the spring becomes?

اس سوال کو وضاحت کے ساتھ پڑھیں

Explanation

A bullet on penetrating 30cm into its target A loses its velocity by 50%. What additional distance will its penetrate into the target before it comes to rest?

اس سوال کو وضاحت کے ساتھ پڑھیں

Explanation

Let L be the length and d be the diameter of B cross section of a wire. Wires of the same material with different L and d are subjected to the same tension along the length of the wire. In which of the following cases the extension of wire will be the maximum?

اس سوال کو وضاحت کے ساتھ پڑھیں

Explanation

The point at which an applied force A produces linear motion but no rotatory motion is _____?

اس سوال کو وضاحت کے ساتھ پڑھیں

Explanation

Average distance of the earth from the sun A is L1. If one year of the earth =D days one year of another planet whose average distance from the sun is L2 will be ______?

اس سوال کو وضاحت کے ساتھ پڑھیں

Explanation

A particle is travelling among a straight line OX. The distance x in meters of the particle from O at a time t is given by X = 37 + 27t t³ where t is given by X in the seconds. The distance of particles from O when it comes to rest is W3.

اس سوال کو وضاحت کے ساتھ پڑھیں

Explanation

Ultra violet light is more likely to cause a photoelectric effect than a visible light. This is because photons of ultraviolet light _____?

اس سوال کو وضاحت کے ساتھ پڑھیں

Explanation

If A = B+C and A,B,C have scalder magnitudes of 5,4,3 unit respectively then the angle between vector A and vector B is _____?

اس سوال کو وضاحت کے ساتھ پڑھیں

Explanation

The dimension formula of angular momentum is?

اس سوال کو وضاحت کے ساتھ پڑھیں

Explanation

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