Three vectors satisfy the relation and then is parallel to
1
2
3
4
Official Solution
Correct Option: (1)
Here = = = O
Similarly, and are in the same plane and
is perpendicular to them.
Thus
02
PYQ 2008
easy
physicsID: kcet-200
If the earth shrinks such that its mass does not change but radius decreases to one quarter of its original value then one complete day will take
1
96 h
2
48 h
3
6 h
4
1.5 h
Official Solution
Correct Option: (4)
We know that angular momentum of spin By the conservation of angular momentum
03
PYQ 2009
easy
physicsID: kcet-200
A door of wide requires a force of to be applied at the free end to open or close it. The force that is required at a point distant from the hinges for opening or closing the door is
1
3.6 N
2
2.4 N
3
4 N
4
1.2 N
Official Solution
Correct Option: (3)
Here, torque So, when ,
04
PYQ 2011
medium
physicsID: kcet-201
A solid sphere of mass rolls down an inclined plane without slipping, starting from rest at the top of an inclined plane. The linear speed of the sphere at the bottom of the inclined plane is . The kinetic energy of the sphere at the bottom is
1
2
3
4
Official Solution
Correct Option: (4)
Take KE at bottom
05
PYQ 2014
easy
physicsID: kcet-201
A force acts on a particle whose position vector is What is the torque about the origin?
1
2
3
4
Official Solution
Correct Option: (1)
Given,
and
We know that So, torque about the origin will be given by,
06
PYQ 2014
medium
physicsID: kcet-201
A rotating wheel changes angular speed from to in . What is the angular acceleration assuming to be uniform ?
1
2
3
4
Official Solution
Correct Option: (3)
We know that
where
Similarly,
If the angular velocity of a rotating wheel about on axis changes by change in angular velocity in a time interval , then the angular acceleration of rotating wheel about that axis is
07
PYQ 2015
medium
physicsID: kcet-201
Moment of Inertia of a thin uniform rod rotating about the perpendicular axis passing through its centre is . If the same rod is bent into a ring and its moment of inertia about its diameter is , then the ratio is
1
2
3
4
Official Solution
Correct Option: (1)
We know that, radius of ring,
Moment of inertia of thin uniform rod,
and same rod is bent into a ring, then its moment of inertia,
From E (i).
On dividing E (ii) by E (iii), we get
08
PYQ 2017
easy
physicsID: kcet-201
Two balls are thrown simultaneously in air. The acceleration of the centre of mass of the two balls when in air,
1
depends on the masses of the two balls
2
depends on the speeds of the two balls
3
is equal to (Acceleration due to gravity)
4
depends on the direction of motion of the two balls.
Official Solution
Correct Option: (3)
We know that, Acceleration of centre of mass
Here, (Because balls are thiown in air i.e. under the gravity)
09
PYQ 2020
medium
physicsID: kcet-202
Two protons are kept at a separation of 10 nm. Let Fn and Fe the nuclear force and the electromagnetic force between them
1
Fe = Fn
2
Fe >> Fn
3
Fe << Fn
4
Fe and Fn differ only slightly
Official Solution
Correct Option: (2)
At a separation of 10 nm, the electromagnetic force between two protons is much larger than the nuclear force . The nuclear force is short-range and is effective only at distances on the order of femtometers (fm), typically around meters, while the electromagnetic force acts over much larger distances. At 10 nm ( meters), the electromagnetic force between the protons is much stronger than the nuclear force, so .
The correct answer is (B) : Fe >> Fn.
10
PYQ 2023
easy
physicsID: kcet-202
A charged particle is subjected to acceleration in a cyclotron as shown. The charged particle undergoes increase in its speed
1
Only inside D2
2
Inside D1, D2 and the gaps
3
Only inside D1
4
Only in the gap between D1 and D2
Official Solution
Correct Option: (4)
Step 1: Basic Principle of Cyclotron:
A cyclotron is a device used to accelerate charged particles to high velocities using a high-frequency alternating electric field and a perpendicular magnetic field.
Important: The magnetic field inside the two hollow semi-circular electrodes (D-shaped chambers, called "Dees") only bends the path of the particle into a circular trajectory but does not increase its speed.
Step 2: Role of Electric Field:
The charged particle gains kinetic energy (and hence increases its speed) only when it crosses the gap between the two Dees, where a strong alternating electric field is applied.
This electric field accelerates the charged particle each time it crosses the gap, thus increasing its velocity.
Step 3: Clarification of given options:
Inside Dees (D₁ and D₂): The particle moves under the influence of a uniform magnetic field. Hence, the speed remains constant inside each Dee.
Between Dees (gap): A strong electric field exists in the gap. Hence, the particle accelerates (increases speed) here.
Thus, the charged particle accelerates (increases speed) only in the gap between the Dees.
Final Answer: Option (D) Only in the gap between and
11
PYQ 2025
medium
physicsID: kcet-202
During an elastic collision between two bodies, which of the following statements are correct?
1
I, II, and III
2
I and II only
3
II and III only
4
I and III only
Official Solution
Correct Option: (4)
In an elastic collision, the two primary conditions are: - Kinetic Energy is conserved: The total kinetic energy before and after the collision remains the same. - Linear Momentum is conserved: The total momentum of the system before and after the collision remains unchanged, provided no external forces act on the system. Let’s evaluate each statement: 1. The initial kinetic energy is equal to the final kinetic energy of the system: - This is true for elastic collisions, as both kinetic energy and momentum are conserved. 2. The linear momentum is conserved: - This is also true in an elastic collision. Linear momentum is conserved unless external forces are involved. 3. The kinetic energy during the collision (the collision time) is not conserved: - This is true in the sense that the total energy remains constant, but energy can be transferred to other forms like heat or sound during the collision process. However, this is not a contradiction because we are concerned with the total system energy, which remains conserved in an ideal elastic collision. Thus, statements I and III are correct. Therefore, the correct option is (4) I and III only.
12
PYQ 2026
medium
physicsID: kcet-202
A mass M is hung with a light inextensible string as shown in figure. Find the tension of the horizontal string.
1
2
3
4
Official Solution
Correct Option: (3)
Step 1: Understanding the Question:
The problem asks for the tension in the horizontal string that supports a mass M, given that another string is inclined at 45 and connected to the same junction. This is a static equilibrium problem. Step 2: Key Formula or Approach:
For a system in equilibrium, the net force in both horizontal and vertical directions is zero.
Let be the tension in the horizontal string and be the tension in the inclined string.
The weight of the mass is . Step 3: Detailed Explanation:
Draw a Free Body Diagram (FBD) for the junction point O where the three strings meet.
- Downwards force: (due to the hanging mass).
- Horizontal force (to the left): (tension in the horizontal string).
- Inclined force: (tension in the string making 45 with the horizontal).
Resolve the inclined tension into its horizontal and vertical components:
- Horizontal component of : (to the right).
- Vertical component of : (upwards). Apply equilibrium conditions:
1. Vertical equilibrium ( ):
Forces acting upwards = Forces acting downwards
2. Horizontal equilibrium ( ):
Forces acting to the right = Forces acting to the left
Substitute and :
Step 4: Final Answer:
The tension in the horizontal string is .
