Physics Test

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Physics Test - 20

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Weekly Quiz Competition

Question 1
1 / -0

Two waves represented by \(y_{1}=10 \sin (2000 \pi t+2 x)\) and \(y_{2}=10 \sin (2000 \pi t+2 x+\pi / 2)\) are superposed at any point at a particular instant. The resultant amplitude is:

A
10

B
20

C
14.1

D
0

Solution

Answer: ICl
The resultant amplitude \(A\) of two waves of amplitudes a
and \(a_{2}\) at a phase difference \(\phi\) is \(\left(\left(a_{1}^{2}+a_{2}^{2}+2 a_{1} a_{2} \cos \theta\right)^{1 / 2}\right.\)
Substituting
\(\mathrm{a}_{1}=10, \mathrm{a}_{2}=10\) and \(\phi=90^{\circ},\) we get \(\mathrm{A}=14.1\)
Question 2
1 / -0

Distance between a frog and an insect on a horizontal plane is 9 m. Frog can jump with a miximum speed of√10m/s . Minimum number of jumps required by the frog to catch the insect is (Take g = 10 m /s²)

A
7

B
8

C
9

D
4

Solution

Range is maximum for \(45^{\circ}\) projection
The distance covered in one hop will be, \(R=\frac{u^{2}}{g}=1 \mathrm{m}\)
Hence, it would take 9 jumps
Question 3
1 / -0

For a satellite escape velocity is 11 km/s. If the satellite is launched at an angle of 600600 with the vertical, then escape velocity would be

A
33 km/s

B
11√3 km/s

C
11√6 km/s

D
11 kms⁻¹

Solution

Escape speed of a body from Earth's surface is given by: \(v_{\min }=\sqrt{2 g R}\) This expression is obtained by conservation of energy and doesn't involve in which direction the body is thrown/projected. So, irrespective of the angle of projection, escape speed of the body from Earth's surface remains constant i.e. \(\approx 11 \mathrm{km} / \mathrm{s}\)
Question 4
1 / -0

A particle P is moving in a circle of radius 'a' with a uniform speed v . C is the centre of the circle and AB is a diameter. When passing through B the angular velocity of P about A and B are in the ratio

A
1 : 1

B
1 : 2

C
2 : 1

D
4 : 1

Solution
Question 5
1 / -0

A car is going with constant speed on a circular path. If it starts from point A at t = 0 and reaches diametrically opposite point B after 2 sec then find its angular velocity.

A
π

B
π/2

C
3π/2

D
2π

Solution

In going from \(\mathrm{A}\) to \(\mathrm{B}\) the car is displaced by an angle of \(180^{\circ}\)
So, angular displacement \(=\pi\) radians
Time \(=2 \sec\)
Angular velocity \(=\frac{\text {angular displacement}}{\text {time}}\)
\(\omega=\frac{\pi \mathrm{rad}}{2 \mathrm{sec}}\)
Question 6
1 / -0

A force has been applied on a ball when it is

A
kicked

B
pushed

C
thrown

D
All of these

Solution

A force has been applied on a ball when it is kicked, pushed, thrown or flicked
Question 7
1 / -0

If the unit of force and length each be increased by four times, then the unit of energy is increased by

A
16 times

B
8 times

C
2 times

D
4 times

Solution

Work = Force×Displacement

If unit of force and length be increased by four times then the unit of energy will increase by 16 times.
Question 8
1 / -0

In the system shown in figure, the pulley is smooth and massless, the string has a total mass 5g, and the two suspended blocks have masses 25g and 15g. The system is released from state l=0 and is studied upto stage l′=0. During the process, the acceleration of block A will be

A
constant g/9

B
constant g/4

C
increasing by factor of 3

D
increasing by factor of 2

Solution

Consider the case when \(l=0\)
Mean, whole of the rope is on the right side
The acceleration of the system will be given by
\(a=\frac{m_{a} g-m_{b} g-m_{r o p e} g}{\text {total mass}}\)
\[
a=\frac{250-150-50}{45}
\]
\(a=\frac{50}{45}\) A moving down and B moving up
Now consider the case when \(l^{\prime}=0\)
Whole rope is on the left side
At that instant, the acceleration of the system will
\[
a=\frac{m_{a} g+m_{\text {rope}} g-m_{b} g}{\text {total mass}}
\]
\(a=\frac{150}{45}\) A moving down and \(B\) moving up
\(=3\) times (when \(l=0\)
Question 9
1 / -0

A body of mass 2kg is projected with an initial velocity of 5 ms⁻¹ along a rough horizontal table.The magnitude of work done on the body by the frictional forces before it is brought to rest is:

A
-250 J

B
-2.5 J

C
-10 J

D
-25 J

Solution

Work done by frictional force
\[
\begin{array}{l}
=\Delta(K . E) \\
=\frac{1}{2} m\left(v^{2}-u^{2}\right) \\
=\frac{1}{2} \times 2 \times-25 \\
=-25 J
\end{array}
\]
Question 10
1 / -0

A solid sphere is rotating in free space. If the radius of the sphere is increased keeping the mass same without applying any external force, which one of the following will not be affected?

A
Moment of inertia

B
Angular momentum

C
Angular velocity

D
Rotational kinetic energy

Solution

\(I=\frac{2}{5} m R^{2}\) (For sphere)
\(I \propto R^{2}\)
\(\therefore\) Moment of inertial will increase
\(\rightarrow\) Angular moment will remain constant as net external torque is zero.

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Physics Test - 20

Result

Physics Test - 20

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SHARING IS CARING

Question 1

10

20

14.1

0

Solution

Question 2

7

8

9

4

Solution

Question 3

33 km/s

11√3 km/s

11√6 km/s

11 kms−1

Solution

Question 4

1 : 1

1 : 2

2 : 1

4 : 1

Solution

Question 5

π

π/2

3π/2

2π

Solution

Question 6

kicked

pushed

thrown

All of these

Solution

Question 7

16 times

8 times

2 times

4 times

Solution

Question 8

constant g/9

constant g/4

increasing by factor of 3

increasing by factor of 2

Solution

Question 9

-250 J

-2.5 J

-10 J

-25 J

Solution

Question 10

Moment of inertia

Angular momentum

Angular velocity

Rotational kinetic energy

Solution

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11 kms⁻¹