1. What is a collision? Mention the types of collisions.
It is the process of mutual interaction between the bodies in which redistribution of momentum takes place is called collision. These are of two types.
1. Elastic collision 2. Inelastic collision
2. Which physical quantity remains constant (i) in elastic collision (ii) in an in – elastic collision.
In an elastic collision both momentum and kinetic energy of the system are constant.
In an in-elastic collision only momentum remains constant
3. Define co – efficient of restitution and state its value in case of elastic and inelastic collisions.
The ration between the relative velocity of separation after collision to the relative velocity of approach before collision is called coefficient of restitution. For two colliding bodies e = (v2 – v2 ) / u1 – u2.
4. Distinguish between elastic and in – elastic collisions?
| Elastic collision | Inelastic collision |
| 1. Both momentum and kinetic energy are conserved | Only momentum is conserved |
| 2. for perfectly elastic collision e = 1 | 2. for perfectly in elastic collision e = 0 |
| 3. the bodies move separately after the collision | 3. the bodies stick together after collision |
| 4. temperature of the system does not change | 4. temperature of system changes |
| 5. Ex: Collision between nuclei & fundamental particles | 5. Ex: Collision between grossy bodies. |
For elastic collision e = 1.
For inelastic collision e = 0.
Very short answer questions.
- What is inertia?
Ans: The resistance of the body to change its state of rest or of uniform motion in a straight line is called INERTIA of the body.
- What is the mass of a body?
The property of the body which determines its resistance to change its state is called the mass of the body.
- “Mass is a measure of inertia” Explain?
We know a = F/m . More is the mass, less is the acceleration and more is the inertia. Thus, mass of a body is a quantitative measure of its inertia.
- State and define the unit of force in SI unit?
F = ma. If, m = 1 kg, g = 1 m /s2. we get F = 1N, and the SI unit of force is newton, and it can be defined as the force which when acting on a body of mass 1 kg produces in it an acceleration of 1 m/s2.
- Are the three laws of
No,
- What is ‘Tension’ in a cable?
The force exerted by the cable at any point inside the cable is called the tension in the cable at that point.
- What is an ideal rope thread)?
The rope which is inextensible, torsion less, frictionless is said to be an ideal rope.
- Can internal forces (force exerted on one part of the system by another part of the system) cause motion?
No.
- Can the passengers in a stationary bus make the bus movie by pushing it? Why?
No, because, internal forces can’t cause motion in the system.
- A sail boat cannot be propelled by blowing air on the sail from a fan in the same boat. Why?
No, because, internal forces can’t cause motion in the system.
- A man sitting in a chair cannot lift the chair by pulling is arms. Why?
No, because, internal forces can’t cause motion in the system.
- The dust particles can be removed from the carpet by beating it. What principle is involved here?
Moment of inertia due to rest.
Explanation: When a quick jerk is given in the carpet, all the dust particles remain at rest and the carpet moves away from it, thus dust particles can be removed.
- Passengers in a moving bus tend to fall forward. When the bus stops suddenly. Why?
Moment of inertia due to motion
Explanation: When the bus is in motion, body of the passenger will be under motion along with the bus. When the bus stops suddenly, feet comes to rest where as his body under motion due to the moment of inertia due to motion, thus the passenger falls forward.
- An athlete runs through a distance before taking a long jump or a high jump. Why?
To overcome the moment of inertia due to rest.
- When a bus suddenly turns towards right the passengers inside are pushed to their left. Why?
Moment of inertia due to direction.
- What is the main purpose served by a pulley?
To change the direction of the tension in the rope.
- What is a resultant force? Find the resultant force when two forces are perpendicular?
The vector sum of the all the forces acting on a particle is equal to the resultant force.
Resultant force = √(F12+ F22 + 2 F1F2 cos θ)
Since they are perpendicular to each other θ = 90° and
Resultant force = √(F12+ F22 ).
- Define impulse and state its SI units?
Impulse is defined as product of the large amount of force and the short time for which the force acts. It is a vector. It has the same direction of force. It is expressed in N – S.
- A man weighs 500 N. A lift carrying him falls freely. What is the apparent weight of the man in the lift?
Zero. Since if the lift is feely falling, a = g.
And W’ = mg = ma = 0.
- When a lift moving up with an acceleration twice that of acceleration due to gravity, what is apparent weight of a person whose real weight is 400 N?
Given W = 400 N; a = 2g;
W’ = mg (1 + a/g)
W’ = mg (1 + 2g / g)
W’ = 400 (3) = 1200 N.
- Calculate the impulse on a body at rest when acted upon by a force of 4N for 2 sec
Impulse = F X t = 4 x 2 = 8 N – S.
- If a lorry and a car moving with some momentum, are brought to rest by applying some resistive force, which travels more distance before coming to rest.?
Car, as F x S = P2/2m, but F1 = F2 AND P1 = P2
Therefore S α 1/m, i.e., the distance traveled is inversely proportional to mass.
- At what point in the path of a vertically projected body, the kinetic and potential energies are same?
Ans : If the maximum height reached by the body is H, both P.E and K.E are equal at a height H/2.
- Two bodies of different masses have the same momentum. Which will have more kinetic energy?
Ans : Lesser mass possesses more K.E . since KE α 1/m.
- “A cricket ball gets deformed when it is continuously hit by a bat”. Why?
Ans : Because the force acting on the ball by the bat in very less time . If the time of impact is less more force is acted on it . therefore it deforms .
- A body having a velocity of 2 m/s has 1 j kinetic energy. What is its mass?
Ans : K.E =1/2 mv2
i.e., ½ m(4)=1,
2m=1 => m = ½ kg.
- What happens to KE of a body when 3/4th of its mass is removed, and velocity is doubled?
Ans: K.E = ½ mv2
Now KE is KE1 ,
KE1=1/2 (m/4)(2v)2 =1/2 m/4 4v2
ð KE1=1/2 MV2
ð It is unchanged.
- Why does a cricketer pulls his hands backwards, while taking a catch?
In order to increase the time of impact thereby receiving a less force on his hands due to the ball
Shock absorbers are fitted to vehicles. Why?
When the vehicles cross overt the speed breakers, the shock absorbers will slowly compress and increase the time of impulse. Thereby the rider travels with less opposing force due to the impact- If KE of a body is equal to momentum. Find its velocity in SI units?
Since kinetic energy of the body is equal to its momentum
½ m v2 = mv
31. When a gun fires a bullet out of the gun, and bullet which will have greater momentum and which will have greater K.E?
The gun & bullet will have same momentum. ( from law of conservation of momentum)
K.E = P2/2m
32.Calculate resultant acceleration when two forces of magnitude 13 N and 5 N , which are perpendicular to teach other act on a 2 kg mass?
A = √ (F12 + F22)/m = √ (132 + 52)/2 = √194 / 2 m/sec 2.
33.What is the distance through which a body moves when a constant force of 5 N acts on it to change its K.E from 17 J to 32?
W = Change in K. E.
F x S = ½ m v 2 – ½ m u 2
5 x S = 32 – 17
S = 3 m.
34. Three forces of magnitude F are acting along the directions North, East and West on a body. What is the magnitude and direction of the resultant force?
Magnitude F and direction North.
Since, the forces in East and West directions will nullify each other.
35. Can a body have finite acceleration and zero KE?
Yes, a body can have finite acceleration even though kinetic energy is zero.
Ex: 1) When simple pendulum or a loaded spring is at its extreme position i.e., at maximum displacement point velocity, v = 0, so, kinetic energy is zero. But it has some acceleration directed towards mean position.
2) For a body released from certain height velocity when dropped is zero. So kinetic energy is zero. But still acceleration due to gravity acts on it.
36. State Law of conservation of linear momentum?
The algebraic sum of momentum before collision is equal to the sum of momentum after collision.
m1u1 + m2 u2 = m1 v1 + m2 v2
37. Distinguish between conservative and non conservative forces. Give one example each?
| Conservative forces | Non – conservative forces |
| 1. The work done in a closed path is zero. 2. The work done depends only upon the locations of the two points and independent upon the path followed | 1. The work done by the force on a body along a closed path is not zero. 2. The work done depends upon the path followed |
| 3.Ex: Gravitational force, The elastic force exerted on by an ideal spring | Ex: Frictional force, Electromagnetic induction |
Lesson wise very short answer questions with answers.
(According to board of intermediate academy text book)
- Units and dimensions and errors and approximations
- Elements of vectors
- Kinematics
- Dynamics
- Collisions
- Center of mass
- Friction
- Rotatory motion
- Gravitation
- Simple harmonic motion
- Elasticity
- Surface tension
- Viscosity
- Thermal expansion of materials
- Thermodynamics
- Transmission of hea
- Can the velocity at any point on the path be zero in the case of a body projected vertically upwards? Explain?
Ans:
yes, at the height point when the body projected vertically upwards.
- Define the maximum height, time of ascent and time of descent for an object vertically thrown up.
Ans:
Max height: The distance traveled by a vertically projected body before its velocity becomes zero.
Time of ascent: The time taken by a vertically projected body to reach the max height is called time of ascent.
Time of descent: The time taken by a vertically projected body to traveled from its max height position to the point of projection is called time of descent.
- Can a body moving in a two dimensional plane has acceleration in only 1 dimension?
Ans:
Yes, in case of oblique projectile the body possesses two dimensional motion, but it has acceleration due to gravity, which is one dimensional.
- Mention the direction of motion the projectile at the point of its max height?
Ans:
At the max height position of a projectile, its direction of motion is horizontal.
- Mention the path of an object which is dropped outside through the window, of a moving vehicle. Why is it so?
Ans:
The path is parabola, because it is like a horizontal projectile, whose horizontal velocity is equal to the velocity of the vehicle with respect to the observer on the ground.
- A stone is thrown horizontally and another is dropped freely from the same height. Which of the two will reach the ground early? Explain?
Ans:
Both reach the ground at the same time. The time of journey is given by t = √ (2h / g). as initial velocity in the downward direction for both the cases is zero.
- For a stone what is the ratio of distances covered in 1st, 3rd, and 5th seconds of its free fall?
Ans:
According to
Sn = u + a (n – ½)
S1 = 0 + g (1 – ½) = g/2
S3 = 0 + g (3 – ½) = 5g/2
S5 = 0 + g (5 – ½) = 9g/2
S1 : S3 : S5 = 1: 5 : 9
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