Matric Notes Physics 9th Ch 2 Kinematics Short Questions

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Conceptual Questions

Q1. What is kinematics? Also, define rest and motion?

Ans. Kinematics:-the branch of physics which deals with the study of the motion of bodies without reference to force is called kinematics.

Rest:-if a body does not change its position with respect to its surrounding then the body is called in a state of rest. For example, a boy is setting in his chair in his classroom .then he does not change his position with respect to his surrounding and we say that boy is in a state of rest.

Motion:– if a body changes its position with respect to its surrounding then the body is called in a state of motion. For example, a cyclist changes his position every moment with respect to his surrounding then we say that cyclist is in state of motion.

Q.2 Discuss types of motion with examples?

Ans. There are three types of motion that are given below.

Translator motion:-  That type of motion in which every particle of a body moves parallel to each other along any path is known as translator motion. For example motion of the car, the motion of airplane motion of birds, and the motion of the boat.

Rotatory motion:– that type of motion in which every particle of a body moves around a fixpoint is known as rotator motion. For example motion of fan, the motion of the wheel, and motion hand ‘s clock.

Vibratory motion:– the to and for the motion of body area the same path about its mean position, is known as vibratory motion. For example motion of a pendulum and motion of a mass attached to a spring.

Q.3 Define some terms associated with motion?

Ans.  Position:- The location of an object relative to some reference point is known as the position of that point.

Distance:- The length of the actual path covered by a body during motion is called Distance it may be straight or curved. It is a scalar quantity and its unit is meter.

Displacement:- The shortest distance b/w any two-point is called displacement. In the opposite figure, AD is displacement while ABCD is covered distance.

Speed:- Distance covered by a body in unit time (1 sec) is called speed.

Mathematical speed = distance covered /time v = s/t

It is a scalar quantity and its unit is m/sec.

i. Uniform speed:- If a body covers equal distance in equal interval of time then the speed is called uniform speed.

ii. Variable speed:– If a body covers unequal distance in equal interval of time then the speed is called variable speed.

iii. Average speed:– Total covered distance divided by total taken time is equal to average speed. math:-total covered distance /total time. <v> = s/t

iv. Instantaneous speed:- The speed of a body at any particular instant of time is known as instantaneous speed. Math:-vins = s/ t where “^s” is the small distance covered in small time

Velocity:- The rate of change of displacement is called velocity.

Mathematics Velocity = displacement / time V =s/t

It is a vector quantity and its unit is m/sec.

i. Uniform velocity:- If a body covered equal displacement in equal interval of time then the velocity is called uniform velocity.

ii. Variable velocity:-if a body covers unequal displacement in equal interval of time then the velocity is called variable velocity.

iii. Average velocity:-total displacement divided by total taken time is equal to average velocity. Math. Average velocity = total displacement /taken time. v = s/t

Acceleration:- The rate of change of velocity is called acceleration.

Math:- acceleration = velocity/time

a =∆v /∆t

It is a vector quantity and its is m/sec.

i. Uniform acceleration:- If velocity of a body changes equally in equal interval of time is called uniform acceleration.

ii. Variable acceleration:- If the velocity of a body changes unequally in equal interval of time is called variable acceleration.

iii. Linear acceleration:- Linear acceleration produced due to change in magnitude of velocity of body.

iv. Radical acceleration:- Radical acceleration is produced due to change in direction of velocity.

v. Negative acceleration:- If the magnitude of velocity decreases with the passage of time then it is called –ve acceleration.

vi. Instantaneous acceleration:- The acceleration of a body at any particular instant of time is known as instantaneous acceleration.

Math:- αins =∆v /∆t where is the small velocity covered in small time “t”.

Q.4 Define and explain scalar and vector quantities with examples?

Ans. Scale quantities :-Those physical quantities which can be completely specified by their magnitude only are called scalar quantity For explanation of scalar quantities we need a number with a proper unit. If any one of them is ignored then our explanations incomplete. Scalar quantities can be add, subtracted, multiplied and divided by ordinary method of mathematics. Speed , distance, mass, power, density, charge, volume current and heat etc are the examples of scalar quantities.

Vector quantity:- Those physical quantities which are completely described by their magnitude as well as direction are called vector quantities for complete explanation of these quantities we need a number unit and also a direction. These three things are very necessary for complete description. If we ignore any one of them then our explanation is incomplete. Velocity, force torque, weight, displacement and

acceleration etc are examples of vector quantities.

Q.5 Can a body at rest be regarded in motion. Give example?

Ans. Yes a body at rest can be regarded in motion. For example a passenger setting in moving bus is in state of rest with respect to other passenger inside the bus but he Is in state motion with respect to things out side of the bus.

Q.6 Is the distance covered by a body may be greater than the magnitude of displacement?

Ans. Yes, the distance covered by a body may be greater than the magnitude of displacement. As shown

in figure where ABCD is the covered distance which is greater the displacement. AB.

Q.7 As it possible that displacement is zero but not distance?

Ans. Yes. It is possible that displacement is zero but not distance as show in figure a body starts from initial point and comes back to its initial point other walking along circular or triangular path. In both cases the displacement is zero but distance is not zero.

Q.8 Under what condition displacement is equal to distance?

Ans. When a body moves from one point to another along a straight line. Then the magnitude of displacement is equal to the distance covered.

Q.9 Can a body have acceleration with zero velocity?

Ans. Yes, a body can have acceleration with zero velocity because when an object is thrown vertically upward it comes to rest at certain height and velocity becomes zero but it comes back down ward and its acceleration is not zero.

Q.10 Can the speed of a body be – ve?

Ans. No the speed of a body cannot be – ve because it depends upon covered distance and take time and these both can never be – ve that’s why speed of a body cannot be negative.

Q.11Is it possible that the velocity of a body be in a direction other than the direction of acceleration?

Ans. Yes, it is possible that the velocity of a body be in a direction other than the direction of acceleration. Foo example a decelerating body has velocity and acceleration both in appoint direction.

Q.12 If an object is stationary is its acceleration necessarily zero?

Ans. The acceleration of a stationary body may be or may not be zero. Because when change in velocity ie ∆v = 0 the a = o/t i.e acceleration is zero but in case of objects thrown vertically upward comes to rest at some height the velocity becomes zero but still has acceleration because of gravity.

Q.13 When the velocity time graph is a straight line parallel to time axis, what can you say about its acceleration?

Ans. When the velocity time graph is a straight line parallel to time axis then the velocity is uniform and a body having uniform velocity has the acceleration equal to zero.

Q14. Is it possible that displacement is zero but not the distance ? Under what condition displacement is equal to the distance? Under what condition displacement is equal to the distance?

Answer: Yes, it is possible that the displacement is zero but distance is not zero.

For example, a student leaves school from point A. He moves 3m north and reaches point B, 5m in the west to reach point C. Then 3m in the south to reach point D and finally 3m to east and comes the same initial point A. Here the path traveled is 3 + 5 + 3 + 5 = 16m. Here path traveled is distance which is 16 m. But the student is in the same point where he was initially hence his displacement is zero as shown in figure below.

The distance and displacement will be equal when a motion of a body from one point to another point is in a straight line.

For example, Suppose a body only moves from ‘O’ to ‘C’, the distance is the actual path covered by the body, while displacement is the shortest distance between ‘O’ and ‘C’. In both cases, it is 25 m.

Q.15) Does a speedometer measures a car’s speed or velocity?

Answer: Car speedometer only measures speed and doesn’t give any information about direction. The difference between speed and velocity is that velocity has a direction (the direction of the instantaneous speed) associated with it. Suppose a car is moving with 50 km/h, it is the speed of a car, but when you specify 50 km/h towards West, then it is the velocity of a car.

Q.16) Is it possible for an object to be accelerating and at rest at the same time? Explain with example.

Answer: We know that the motion and rest are not absolute but relative.

As,                              acceleration = a = change in velocity / elapsed time

and                                 velocity = v = displacement / elapsed time

Since, acceleration is indirectly dependent on displacement if the body is at rest with respect to some observer, it’s displacement is zero with respect to that observer, in the situation acceleration should be zero with respect to that observer, in this case it is not possible for an object to be accelerating and at rest at the same time.

But if we have a relative motion then for the same event two observers can have different observations. For example, a body in the bus is accelerating with respect to an observer on the ground. Whereas the same body is at rest and have acceleration zero with respect to another observer sitting inside the bus.

Q.17) Can an object have zero acceleration and non zero velocity at the same time? Give example.

Answer: Yes we can have zero acceleration and non zero velocity in case of uniform motion in which an object is moving in straight line with constant velocity, here object has non zero velocity but there is no change in velocity so no acceleration.

Q.18)  A person standing on the roof a building throws a rubber ball down with a velocity of 8.0m/s. what is the acceleration (magnitude and direction)of the ball?

Answer: As we know that all bodies falling toward earth with a constant acceleration of g = 9.8 m/s2. Now a person standing on the roof a building throws a rubber ball down with a velocity of 8 m/s. The acceleration of the ball will be g = 9.8 m/s2 directed toward the earth.

Q.19) Describe the situation in which the speed of an object is constant while the velocity is not.

Answer: Suppose an object moving in uniform circular motion. The speed of the body will be uniform while the direction of body change at every point, therefore the velocity of the body is changing at each point. In this situation, the speed of an object is constant while the velocity is not constant.

Q.20) Can an object have a northward velocity and a southward acceleration? Explain.

Answer: Yes, an object can have northward velocity and a southward acceleration, this is possible when a body is moving towards the north and gradually its velocity decreases. Now the acceleration which is actually the deceleration produced will be in the southward direction.

Q.21) As a freely falling object speeds up, what is happening to its acceleration-does it increases, decreases, or stay the same?  

Answer: The acceleration of a freely falling object remains constant and is  9.8 m/s2, therefore as a freely falling object speeds up, its acceleration will not increase or decrease but will remain the same i.e. 9.8 m/s2.

Q.22) A ball thrown vertically upward with an initial speed of 5 ms-1. What will its speed be when it returns to its starting point?

Answer: In case of no air resistance, the ball will reach its initial position at the same speed of 5 m/s which is the speed with which the ball was thrown vertically upward.