What is Force?
As a trait of physical action or movement, the Force can be defined as a push or pull acting on a body. This generally happens when two objects are in contact. Every object or body in this universe applies a force on other objects according to the universal law of gravitation. The following parameter gives the information about the Force acting on an object:
Newton(N) or kg.m/s2 is the SI unit of Force
Force is denoted by: F
Force is a vector quantity because it talks about both magnitude and direction.
The dimensional formula for Force is: M^{1}L^{1}T^{-2}
Read More:Force and Motion
What is Motion?
In simple words, the change in position of a body with respect to time and its environment is called in motion. For example, if a girl is walking down the street from school to her home, we can say that the girl is in motion. But imagine if the girl stops for 2 minutes in the way, then there will be no movement. Hence, we can say that the motion of the girl is time-dependent.
Hence, we can conclude that the change in position of a body with respect to time is motion. Since the Force causes motion, we can also say that the force and motion are extremely related to each other.
The Formula for Force and Motion
The relationship between Force and motion can be mathematically expressed using Newton’s second law of motion:
The product of mass m and acceleration a is known as Force which is given as:
F = m x a
Using laws of motion, the behaviour of a particle in motion can be explained as:
s = s0 + v0t + ½ at^{2}
Where,
The position of the particle = s
The initial position of the particle = s0
The initial velocity of the particle = v0
Acceleration = a
Time = t
Important Questions on Force and Motion
1) Force is a polar vector.
a) True
b) False
Correct Option: (a)
Explanation: The force is a push or a pull that has a tendency to change the state of rest or of uniform motion of a body, which means that force is a polar vector that has a point of application.
2) In the absence of an external field, what will happen to the body moving along a straight path?
a) The body will stop
b) The body will be moving with the same speed on a different path
c) The body will be moving with the same speed along the same straight path
d) None of these
Correct Option: (c)
Explanation: Even in the absence of external forces, a body moving along a straight path will continue to move in the same direction with the same speed; as stated by Galileo that on a horizontal plane, an object should move with a constant velocity in a straight-line path.
3) Displacement is a vector quantity.
a) True
b) False
Correct Option: (a)
Explanation: The change in a position of an object in a fixed direction is known as displacement, which means that displacement has both magnitude and direction. Therefore, displacement is a vector quantity.
4) A person sitting inside a moving bus_____ when it suddenly stops.
a) Falls backward
b) Falls down
c) Falls forward
d) Remain unaffected
Correct Option: (c)
Explanation: The lower part of the person’s body comes to rest along with the bus as the bus stops, whereas due to inertia, the upper part of his body continues to remain in motion, and therefore the person falls forward.
5) What will happen if a wolf chases a rabbit and the rabbit runs in a zigzag path?
a) The wolf gets confused
b) The wolf catches the rabbit easily
c) It becomes tough for the wolf to catch the rabbit
d) The rabbit dies
Correct Option: (c)
Explanation: It becomes tough for the wolf to catch the rabbit, when it runs in a zigzag path because, as compared to the rabbit, the wolf has more mass and hence has more inertia of direction.
6) On a level road, if a bike is moving along a zigzag path, then which among the following motion can be observed?
a) Uniform motion
b) Two-dimensional motion
c) Non-uniform motion
d) One-dimensional motion
Correct Option: (b)
Explanation: If the change in position with respect to time is specified by only two coordinates, then the motion of an object is said to be two dimensional. Therefore, the bike moving in a zigzag path on a level road is an illustration of two-dimensional motion.
7) Calculate the average speed of a car travelling from A to B at 50m/s and from B to A at 70m/s.
a) 0
b) 58.82 m/s
c) 240 m/s
d) 3.5 m/s
Correct Option: b
Explanation: To travel from A to B and then from B to A, total time taken by the car can be calculated as:
t_{1}+t_{2} = AB/50 + AB/70 = 0.034 AB
Total distance covered = AB + BA = 2AB
Average speed = 2AB/(t_{1}+t_{2}) = 58.82 m/s.
8) If a bus is approaching a bus stop, what will be its acceleration?
a) Uniform acceleration
b) Non-uniform acceleration
c) Positive acceleration
d) Negative acceleration
Correct Option: (d)
Explanation: When a bus approaches its stop, its acceleration decreases; therefore, we can conclude that if the velocity of an object decreases with time, its acceleration becomes negative. Therefore, it has negative acceleration.
9) Calculate the minimum length of the runway, if a jet plane makes a run for 40 s before taking off, and also it starts from rest with an acceleration of 5 m/s^{2}.
a) 1000 m
b) 1800 m
c) 2400 m
d) 4000 m
Correct Option: (d)
Explanation: Minimum length of the runway can be calculated by:
s = ut + 1/2 at^{2} = 0 + 1/2 × 5 × 40 × 40 = 4000 m.
10) Which among the following can be observed as an example of motion in three dimensions?
a) Planets revolving around the sun
b) Train moving along a straight track
c) A free-falling body
d) A kite flying in the sky on a windy day
Correct Option: (d)
Explanation: If all the three coordinates specifying the position of an object change with respect to time, then the motion of an object is said to be three dimensional. Therefore, a kite flying in the sky on a windy day is a perfect example of motion in three dimensions.
Practice Questions
1) Define force.
2) Define motion.
3) What is uniform motion?
4) Define acceleration.
5) What is uniform velocity?
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