Polytechnic physics semester 1 chapter 1 measurement and force,question answers.
Questions And Answers :-1)what do we mean by physical quantity?
Ans:physical property related to a substance or phenomenon which can be quantified by measurement is called a physical quantity.
2)what is unit?
Ans:The standard used for the measurement of a physical quantity is called unit.
3)what is fundamental quantities and derived quantities?
Ans:physical quantities which are defined by process of measurement and independent of other quantities are called fundemental quantities.
-quantities derived from fundemental quantities are called derived quantities.
4)3 Examples of unit system?
Ans:CGS, MKS, SI
5)what are the Fundamental quantities and their units in SI unit system?
Ans:Length-meter
Mass-kilogram
Time-second
Electric current-Ampere
Temperature -kelvin
Amount of substance -mole
Luminous intensity -candela
6)what is error in measurement's?
Ans:The difference between the true value and the measured value of a quantity is known as the error of measurement.
7)explain classification of error in measurements?
Ans:Systematic Errors
Systematic errors in measurements can be due to instrumental errors, incorrect experimental techniques, and personal errors.
a) Instrumental errors: These errors arise from the imperfect design or calibration of instruments, zero error of instruments, etc. Zero error in vernier calipers or screw gauge and error due to measurement of length using a scale broken at one end are examples of instrumental errors:
b) Error due to incorrect experimental technique: These kinds of errors occur due to inaccurate experimental procedures as well as external factors like pressure, temperature, humidity, wind, etc. For example, measurement of body temperature by placing a thermometer under the armpit results in a lower temperature value than the actual value.
c) Personal errors: Such errors arise due to personal bias, lack of proper setting of the apparatus, or individual's carelessness in taking observations. These types of errors are also known as observational errors. For example, when an observer holds his head towards the right (by habit) while reading the position of a needle on the scale, be introduces an error due to parallax.
Random Errors
Random errors come from unpredictable changes in experimental conditions. The magnitude and direction of these errors vary randomly with each measurement. Random errors are present in all experiments and are unpredictable. The random errors can be reduced by taking a greater number of measurements. These errors are also called statistical errors and can be removed by statistical methods like averaging. For example, unpredictable temperature changes can affect the electrical properties of instruments in an experiment involving electrical instruments.
1.2.3 Least Count Error
The least count error is the error associated with the resolution of the instrument. The smallest value that can be measured by a measuring instrument is called its least count. All readings or values are good only up to this value For example, a vernier caliper has the least count of 0.01 cm and a screw gauge has a least count of 0.001 cm. Using instruments of higher precision, improving experimental techniques, etc, we can reduce the least count error. Repeating the observations several times and taking the arithmetic mean of all the observations, the mean value would be very close to the true value of the measured quantity
1.2.4 Absolute error
Leta,.............abe the values obtained for a physical quantity 'a' in an experiment repeated 'n' times. The arithmetic mean of the values is taken as the true value. The arithmetic mean is
amean= a1+a2..........+an
___________________
n
The absolute error of a measurement is the difference between the individual measurement and the true value of that quantity. It is denoted as |^a|Then errors in individual measurements are
^a1=amean-a1
^a2=amean-a2
..............................
^an=amean-an
1.2.5 Relative error
The ratio of mean absolute error, Aamran to the mean value, amean of the physical quantity measured is called the relative error.
Relative error= ^amean
__________
amean
1.2.6 Percentage error
The relative error of a physical quantity expressed in percentage is called percentage
error.
Percentage error=^amean
__________×100%
amean
8)what is scalar quantity and vector quantity?
Ans:Quantities having only magnitude are called scalar quantities.Quantities having both magnitude and direction are called vector quantities.
9)explain collinear vector, equal vector, negative of a vector?
Ans:1.3.2 Collinear vectors
Two or more vectors lying on the same line are called collinear vectors. They can have the same or different magnitude and the direction can be either the same or opposite.
1.3.3 Equal vectors
Two vectors of the same magnitude and direction are called equal vectors.
1.3.4 Negative of a vector
The negative of a vector is defined as another vector having the same magnitude but opposite in direction to the given vector.
10)explain triangle method of vector addition?
Ans:Triangle method of vector addiction
The triangle method is based on the triangular law of vector addition. The triangular law of
vector addition states that if two vectors are represented by the adjacent sides of a triangle taken
in order, then the resultant vector is represented both in magnitude and direction by the third
side of the triangle taken in the reverse order.
Let A and B are two non-parallel vectors. To find the vector sum using the triangle method , place the vectors such that the tail of one vector coincides with the head of the other tr as shown in Fig 13. Complete the triangle by drawing the third side. The third side gives resultant vector R.
11)explain parallelogram method of vector addition?
Ans:Parallelogram method of vector addition
This method is based on the parallelogram law of vector addition. The parallelogram law vector addition states that if two vectors are represented both in magnitude and direction by e two sides of a parallelogram drawn from a point, then the resultant vector is represented th in magnitude and direction by the diagonal of the parallelogram passing through the point.
In this method, the two vectors are placed such that their tails coincide as shown in Fig. 1.4. A parallelogram is formed by drawing two lines parallel to the given vectors. The diagonal of the parallelogram passing through the common point of the two vectors is the resultant vector.
12)what is resolution of vector, give real life example?.
Ans:The process of splitting a given vector into two or more vectors along different directions is called the resolution of a vector.
Now let us examine two real-life examples of the resolution of vectors.
a) Walking: While walking, a person applies a force on the ground and the reaction force by the ground on the man enables him to move forward. The force applied by the man is directed at an angle with the horizontal. The reaction force by the ground is opposite in direction to the applied force. The reaction force R can be resolved along horizontal and vertical components
b)Pulling a cart :Consider a man pulling a cart. The force is directed at an angle with the horizontal. Here the force can be resolved into two components- vertical and horizontal components as shown in Fig 1.10. The horizontal component is responsible for the motion of the can.
13)Define distance and displacement?
Ans:Distance is defined as the total length of the path travelled by a particle.Displacement is defined as the shortest path length between the final position and the initial position of the particle.
14)Define speed, velocity, acceleration?
Ans:Speed
The speed of a particle is related to the distance travelled. Speed is the distance travelled by a body in unit time.
speed= distance /time
Speed is a scalar quantity and its unit is m/s
Velocity (v)
The velocity of a particle denotes how fast it is changing its position. The displacement of a body in unit time is called velocity.
velocity= displacement/time
Velocity is a vector quantity and its unit is m/s.
Acceleration (a)
The rate of change of velocity of a body is called acceleration. Since velocity is a vector quantity, a change in its magnitude or direction or both gives accelerated motion. acceleration = change in velocity/time
where u is the initial velocity and v is the final velocity of the body. Acceleration is a
vector quantity and its unit is m/s²
15)equations of motion?
Ans:v=u+at
s = ut+1/2at²
v ²= u² + 2as
16)state newtons first law of motion?
Ans:Newton's first law of motion
Newton's first law of motion states that everybody continues in Its state of rest or of
uniform motion along a straight line unless compelled by some external force to change that state.
17)Define force?
Ans:Force can be defined as any agency which can change the state of rest or uniform motion of a body.
18)Define inertia with real life example?
Ans:Inertia
Inertia is the resistance of a body to any change in its state of rest or uniform motion along a straight line.
Real life examples:-
a) A person standing in a stationary bus falls backward when the bus starts suddenly. This is because the lower part of his body moves forward with the bus, but the upper part of his body remains at rest due to inertia of rest, which results in the backward fall.
b) A person trying to get down from a moving bus falls forward. The lower part suddenly comes to rest on touching the ground, but the upper part of his body remains in motion due to inertia of motion and the person falls forward,
c) Fruits from a tree fall due to inertia of rest when the tree is shaken. Both the fruits and
branches are at rest, but when shaken branches start moving whereas fruits remain in its
state of rest and are separated from the branches.
19)what is momentum?
Ans:Momentum (p)
Momentum is the quantity of motion of a body. The momentum of a body is defined as the product of mass and velocity. It is a vector quantity and its unit is kg m/s. If a body of mass "m" moving with a velocity V, then its momentum is given by
p=mv
20)state newtons second law?
Ans:Newton's second law of motion
Newton's second law of motion states that the rate of change of momentum of a body is directly proportional to the applied force and takes place in the direction of the force
21)state Newton's third law of motion?
Ans:Newton's third law of motion
Newton's third law of motion states that to every action, there is always an equal and
opposite reaction.
22)explain law of conservation of momentum?
Ans:from Newton s second law of motion, the net force acting a system of particle is given by
Force= change in momentum
------------------------------------------
Time
final momentum initial momentum
Thus, the law of conservation of momentum states that if the net external force acting on a system is zero, its linear momentum remains constant
As an example, we are going to prove the law of conservation of linear momentum in the case of collision of two masses using Newton's second law and third law. Consider two bodies of masses m, and my moving along a straight line with velocities u, and u, respectively. Let the bodies collide for a time t seconds. After the collision, the velocities become v₁ and Prespectively for masses m, and malong the same direction as shown in Fig. 1.13.
23)explain the recoil of gun. Derive an expression for the recoil velocity of gun?
Ans:The backward motion of a gun when a bullet is fired from it is called the recoil of the gun. It can be explained using the principle of conservation of linear momentum.
24)what is impulse?
Ans:Impulse is defined as the product of force and time for which the firce act.
Impulse=force×time
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