RBSE Class 11 Physics Notes Chapter 3 Motion in a Straight Line

These comprehensive RBSE Class 11 Physics Notes Chapter 3 Motion in a Straight Line will give a brief overview of all the concepts.

RBSE Class 11 Physics Chapter 3 Notes Motion in a Straight Line

Frame of Reference:
Any stationary point or place with respect to which, the position, velocity, acceleration etc. of an object are measured, is called ‘Frame of Reference’.

These are of following three types:

• Cartesian frame of reference
• Spherical frame of reference
• Cylindrical frame of reference.

State of Rest:
If the position of an object does not change with respect to a frame of reference, then the object is said to be in state of rest.

State of Motion:
If the position of an object changes with time with respect to a frame of reference, then it is said to be in state of motion.

Types of Motion:
There are three types of motion:

• Translational motion,
• Rotational motion,
• Vibrational motion.

Motion in a Straight Line:
If an object moves in straight line, then this motion is called motion in a straight line.

Distance and Displacement:

• Distance: The length of path actually adopted by moving body is called distance. It is scalar quantity.
• Displacement: The minimum distance between initial and final positions of the body is called its displacement. It is vector quantity.

Speed:
The distance travelled per unit time, is called speed, i. e. rate of change of distance with time is called speed. It is scalar quantity.

Velocity:
Rate of change of displacement is called velocity. It is vector quantity.

Acceleration:
Rate of change of velocity is called acceleration i.e.,
Acceleration = \(\frac{\text { Change in velocity }}{\text { Time }}\)

• Slope of distance-time graph provides speed and that of displacement-time graph provides velocity.
• The area covered by graphical line and time axis in acceleration-time graph provides the velocity of the object, i.e. \(\vec{v}=\int_{t_1}^{t_2}\)a.dt

 

Stopping Distance of Vehicles:
The distance travelled by a vehicle after applying the breaks and before becoming at rest, is called stopping distance.

Reaction Time:
The time between observing an event and reacting accordingly is called reaction time.

Relative Velocity:
The measurement of velocity of an object with respect to other moving object is called relative velocity, i.e. relative velocity of B with respect to A.
V_BA = V_B - V_A

→ Instantaneous speed v = \(\frac{d S}{d t}\)

→ Instantaneous velocity \(\vec{v}=\frac{v \vec{S}}{d t}\)

→ Average speed
v_av = \(\frac{\text { Totaldistance }}{\text { Total time }}=\frac{S_1+S_2+S_3+\ldots .}{t_1+t_2+t_3+\ldots \ldots}\)

→ Velocity of the particle by acceleration-time graph,
v_av = \(\frac{S}{\frac{S_1}{v_1}+\frac{S_2}{v_2}+\frac{S_3}{v_3}+\ldots}\)

→ When time is constant then
v_av = \(\frac{v_1+v_2+v_3+\ldots \ldots+v_n}{n}\)

→ Acceleration, a = \(\frac{\text { Change in velocity }}{\text { Time }}=\frac{v-u}{t}\)

→ Instantaneous acceleration, a = \(\frac{d v}{d t}=\frac{d^2 S}{d t^2}\)

→ Slope of displacement-time graph provides velocity
v = tan θ = \(\frac{d x}{d t}\)

→ Displacement of the particle in velocity - time graph,
\(\overrightarrow{\Delta S}=\int_{t_1}^{t_2} v \cdot d t\)

→ Velocity of the particle by acceleration-time graph,
\(\vec{v}=\int_{t_1}^{t_2} a \cdot d t\)

→ Equation of uniformly accelerated motion,

• v = u + at
• S = ut + \(\frac{1}{2}\) at²
• v² = u² + 2aS

→ Distance travelled in tth second.
St^th = u + \(\frac{1}{2}\)a(2t - 1)

→ Reaction time, t = \(\sqrt{\frac{2 d}{g}}\)

→ Relative velocity,

• Relative velocity of A with respect to B
  V_AB = V_A - V_B
• Relative velocity of B with respect to A,
  V_BA = V_B - V_A

→ Stopping distnace of vehicles
S.D = \(\frac{u^2}{2 a}\)

→ Frame of reference: Any stationary point or place with respect to which the position, velocity, acceleration etc. of an object are measured, is called frame of reference.

→ Distance: Length of path actually adopted by a moving body is called distance.

→ Displacement: Minimum distance between initial and final positions is called displacement.

→ Speed: Rate of change of distance with time is called speed.

→ Velocity: Rate of change of displacement with time is called velocity.

→ Acceleration: Rate of change of velocity with time is called acceleration.

→ Stopping distance: The distance travelled by the moving vehicle after applying breaks upto becoming at rest, is called stopping distance.

→ Relative velocity: The velocity of a moving object measured by moving observer is called relative velocity.