What is Motion in a Straight Line?
As we know, the change in position of a body with respect to time and its environment is called in motion. Therefore, as the name suggests, motion in a straight line is basically a linear motion in a certain straight line. Hence, motion in a straight line uses one dimension only.
Types of Linear Motion
The motion in a straight line, also entitled the rectilinear motion, is of two types:
- Motion with zero acceleration and constant velocity is Uniform linear motion.
- Motion with non-zero acceleration or flexible velocity is Non-Uniform linear motion.
As suggested by Newton’s first law of motion, an object will either be at rest or continue its motion with a uniform velocity in a straight line unless and until some external unbalanced force is applied to it. Hence, in the same way, linear motion is related to this law, as it is the most straightforward kind of one-dimensional motion.
General motion and linear motion should not confuse you because, as stated above, linear motion is a one-dimensional motion. Overall, the motion has both direction and magnitude; that is, an object’s velocity and position are described in vector quantities.
Uniform Motion in a Straight Line
If a body travels an equal amount of distance in an equal gap or interval of time in a straight line, then it is said to have uniform motion. In simple words, if the rate of change of the velocity of a body remains constant, then the body is said to have uniform acceleration.
Non-uniform Motion in a Straight Line
If the velocity of a body varies unequally in equivalent gaps or intervals of time, then the body is said to have a non-uniform motion. Hence, we can say that the rate of change of its velocity variates at different points of time during its motion.
Important Questions on Motion in a Straight Line
1) If the total displacement is divided by the total time taken, which of the following will be obtained?
a) Speed
b) Acceleration
c) Uniform velocity
d) Average Velocity
Correct Option: (d)
Explanation: Since velocity is said to be uniform when at every instant of time the velocity is equal to the average velocity, speed is the total distance divided by time, acceleration is obtained by velocity divided by time, and the average velocity is attained when total displacement is divided by the total time taken.
2) What kind of energy does a body possess when it is in the state of complete rest?
a) Kinetic energy
b) Potential energy
c) Thermal energy
d) Electrical energy
Correct Option: (b)
Explanation: There is no motion when a body is in a state of rest. Therefore, there will be no kinetic energy, and as we know, the sum of kinetic and potential energies is the total energy. Hence the total energy stored in the body will be potential energy.
3) Rectilinear motion is said to be what kind of motion?
a) Four dimensional
b) Three dimensional
c) One dimensional
d) Zero dimensional
Correct Option: (c)
Explanation: Since the linear motion, also entitled the rectilinear motion, happens in a straight line, it uses one dimension only. Therefore, rectilinear motion is one dimensional.
4) Which among the following forces can probably act on a body whose motion is in a straight line?
a) Force of friction
b) Tangential force
c) Magnetic force
d) Centrifugal force
Correct Option: (a)
Explanation: Since no surface in the world of physics is frictionless, whenever a body is in motion, the force of friction acts on it. And rest, all the given forces act on the body under some special conditions, like when it moves along a curve, and the magnetic force acts on a body when placed in a magnetic field.
5) Which among the following types of motion does not define the motion of the hand of a clock?
a) Rectilinear or linear
b) Periodic
c) Harmonic
d) Circular
Correct Option: (a)
Explanation: The motion of a hand of a clock is not a rectilinear motion, as it exhibits circular motion, because it moves in a circular manner. Furthermore, this motion also occurs periodically, so it is also a periodic motion too.
6) Calculate the velocity of a body that is vertically thrown upwards to a height of 20 m, and the time taken by the object to reach the highest point.
Distance travelled, s = 20 m
Final velocity, v = 0 m/s
g = -9.8 m/s2
Using, v2−u2 =2gs
u2 =392
u=19.79m/s, the velocity with which the object is thrown upwards.
Now, using,
v=u+gt
= t = (v−u)/g = 2.02 sec
7) Define uniform motion in a straight line.
If a body travels an equal amount of distance in an equal gap or interval of time in a straight line, then it is said to have uniform motion. In simple words, if the rate of change of the velocity of a body remains constant, then the body is said to have uniform acceleration.
8) What is non-uniform motion in a straight line?
If the velocity of a body varies unequally in equivalent gaps or intervals of time, then the body is said to have a non-uniform motion. Hence, we can say that the rate of change of its velocity variates at different points of time during its motion.
9) What is motion in a straight line and its types?
As we know, the change in position of a body with respect to time and its environment is called in motion. Therefore, as the name suggests, motion in a straight line is basically a linear motion in a certain straight line. Therefore, motion in a straight line uses one dimension only.
Types of Linear Motion
Uniform motion
Non-uniform motion
10) From the top of a multi-storey building, a ball is thrown vertically upwards with a velocity of 30m/s. In how much time the ball will hit the ground, if the height of the point from where the ball is thrown is 20 m from the ground? Take g=10ms−2.
We can use v=u+at to calculate the time required by the ball to reach maximum height:
0=30+(−10) t
t=3sec
Since, s = ut+0.5at2
= 30(3) +0.5(−10) (3)2 = 45m
Therefore, for maximum height, the total distance is (45+20) m
Now, s = ut+0.5at2
65=0+0.5(10) (t′)2
t′ =3.60sec
Total time= 3.60 + 3= 6.60sec
Practice Questions
- Define motion.
- What are the three equations of motion?
- Give examples of uniform and non-uniform motion.
- What is circular motion?
- What is uniform acceleration?
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