According to the first law of motion, a body at rest will remain at rest or in motion until and unless some external unbalanced force acts on it. The product of its mass and acceleration is equal to the force acting on the body; this is the second law of motion. Newton’s second law explains how much an object will accelerate. Newton’s third law of motion describes the result or outcome of a body when it exerts a force on another body. These forces are equal in magnitude and opposite in direction. There is an equal and opposite reaction for every action, which is stated in the third law. This means that reaction forces can be calculated using the third law of motion.
Important Questions on Laws of Motion
1) Inertia is related to which of the following laws of motion?
a) Zeroth Law of motion
b) Second Law of motion
c) First law of motion
d) Third Law of motion
Correct Option: (c)
Explanation: According to the first law of motion, a body at rest will remain at rest, and a body in motion will remain in motion until and unless some external unbalanced force is applied to it. This law is also identified as the law of inertia.
2) Which of the following Newton’s laws of motion can be used to calculate the force on a body?
a) Zeroth Law of motion
b) Second Law of motion
c) First law of motion
d) Third Law of motion
Correct Option: (b)
Explanation: The net force applied on a body is directly proportional to the rate of change of momentum; this is stated in the second law of motion. Hence, the second law of motion can be used to determine the force on a body.
3) Which of the following Newton’s laws of motion can be used to determine the Reaction forces on a body?
a) Zeroth Law of motion
b) Second Law of motion
c) First law of motion
d) Third Law of motion
Correct Option: (d)
Explanation: Since for every action, there is an equal and opposite reaction, as stated in the third law, this means that reaction forces can be calculated using the third law of motion. One of The best examples of this is the way we walk because when we walk, we need to push the ground when we walk. Therefore, while doing so, an equal and opposite force is experienced by us.
4) Which among the following is the correct mathematical representation of Newton’s second law of motion?
a) F = dq/dt
b) F = m*a
c) F = m/q
d) F = (mv)/r2
Correct Option: (b)
Explanation: F = m*a is the mathematical expression for Newton’s second law of motion.
5) In still water, when a person walks on a boat, what will happen to the boat’s motion?
a) Boat will move ahead
b) Boat will move backwards
c) No motion of the boat
d) Boat will move sideways
Correct Option: (b)
Explanation: The boat will move backwards because the third law of motion is applicable in this case. Since, for every action, there is an equal and opposite reaction, as stated in the third law, the boat experiences an equal and opposite reaction force.
6) Which among the following activities is not an example of the third law of motion?
a) Running
b) Skiing
c) Cycling
d) Walking on a boat
Correct Option: (b)
Explanation: Skiing does not apply any force on the ground; therefore, the third law of motion is not applicable here. The motion in skiing is produced by gravity and very less friction.
7) Explain why a cricketer moves his hands backwards while holding a catch.
A cricketer moves his hand to increase the impact of the ball that is shot by the batsman, so that the force of the ball gets reduced to a comfortable limit without causing injury to the hands.
8) If the mass of a bus is 2000 kg, what will the force required to speed up a bus at the 6ms–2?
According to the question:
Acceleration (a) = 6m/s2 and Mass (m) = 2000 kg, therefore, Force (F) =?
According to the formula, F = m x a
= 2000 kg x 6m/s2
= 12000 kg m/s2
Therefore, required Force = 12000 N
9) A car moving with a speed of 120Km/h along a straight highway and is brought to rest within a distance of 150m. How long does it take for the car to stop? Also, calculate the retardation of the car.
Given,
Velocity of car v=120 km/h = 33.33 m/s
Displacement s = 150 m
Final velocity v = 0 m/s
Applying second equation of motion to calculate retardation a
v2−u2 = 2as
⇒ 0 – (33.33)2 = 2(a) (150) = 3.70 m/s2
Now, by applying the first equation of motion to calculate time t
v=u+at
⇒ 0 = (33.33) + (-3.70) t = 9.00 sec
Hence, retardation is 3.70 m/s2, and the time take to stop is 9.00 sec
10) A car starts from rest and in 30 seconds attains a speed of 50 m/s. Then, it travels at the same speed for 20 seconds. Find the total distance travelled, acceleration and distance travelled during acceleration.
Here, u = 0m/sec, v = 50m/s, t = 20sec and a =?
Since, v = u+at
⇒ 50 = 0 + (a) 20
⇒ a = 2.5 m/s2
Now, to calculate the distance travelled;
s = ut + ½ at2
⇒ s = 0 + ½ (2.5) (20)2
⇒ s = 500m
Now, for total distance travelled;
⇒ st = (vt) + s
⇒ st = (50 * 20) + 500
⇒ st = 1000 + 500 = 1500m
Practice Questions
1) State Newton’s laws of motion.
2) Derive all three equations of motion.
3) What is the difference between speed and velocity?
4) Define Displacement.
5) What is uniform motion?
Top 10 Most Important and Expected Questions on Laws of Motion.
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