Laws of Motion MCQs with Answers

Ans. (D) 0

Explanation: The kite's net force when it is kept still in the sky is zero (0) because, according to the first law of motion stated by Newton, “Unless an external force acts on an item, it remains in a state of rest or uniform motion.” Here, the kite is still and no external force is acting on it, thus, the net force is zero.

Ans. (D) Becomes Zero (0)

Explanation: According to the first law of Newton, “Unless an external force acts on an item, it remains in a state of rest or uniform motion.” Force is directly proportional to momentum. Here, the force is zero, so the velocity is constant, which results in no momentum. Thus, the answer is zero because no momentum will be found.

Ans. (B) Impulsive force

Explanation: An impulsive force is a strong force that acts on an object for a short duration to cause a finite change in momentum. Like all other forces, impulsive force only operates on objects for a short time and in huge quantities.

Ans. (C) 15 km

Explanation: The aircraft's tilt angle is determined by,

Tanθ = v₂ rg

Here, θ denotes the aircraft's angle of tilt, r represents the loop's radius, v denotes its speed, and g is the acceleration brought on by gravity.

Change the values in the equation above.

((720 km/h)(1 h 3600 s)) 2 ((10 m)(1 km 1000 m)) tan(15°) ≈15 km = r

Consequently, the loop's radius is 15 km.

Ans. (D) Inertia

Explanation: A body at rest remains at rest, and a body in motion continues to move at a constant speed if the net external force is zero. The term "inertia" refers to this quality of the body. "Resistance to change" is what inertia refers to. A body does not alter its state of uniform motion or rest until compelled to do so by an outside force.

Ans. (B) 2:5

Explanation: F = ma 

The same force is acting on both masses.

F = m₁ a₁ = m₂ a₂ = constant 

(a₂ / a₁) = (m₁ / m₂) 

Also, v = vo + at 

Here, vo = 0 

v = at 

v = a₁ t₁ = a₂ t₂ = constant 

(t₁ / t2) = (a₂ / a₁) 

Hence, (t₁ / t₂) = (a₂ / a₁) = (m₁ / m₂) = (2 / 5) = 2:5 

Ans. (A) Dynamics

Explanation: The study of motion and forces is known as dynamics. In more formal terms, dynamics is the branch of mechanics concerned with the effect of forces on the motion of objects. Dynamics is meant to imply change. Dynamics is the study of how objects move in relation to the forces, masses, momentum, and energies that influence them.

Ans. (D) All of the above

Explanation: Inertia is of three types:

• The inertia of rest: A body is at rest because of the internal inertia (opposing force) it contains until and unless an external force applied to it exceeds the inertial force.
• The inertia of direction: A body travelling in one direction will continue to move in that same direction unless more force is given to cause the body to move in a different direction.
• The inertia of motion: Until and unless an external force (such as brakes, friction, etc.) is applied to the body, a moving object continues to move.

Ans. (B) Force

Explanation: The second law of motion states that mass and acceleration combine to create force. The general circumstance in which there is a net external force operating on the body is described by the second law of motion. It connects the body's acceleration to the net external force.

Ans. (B) 2

Explanation: Assuming acceleration is ‘a’,

Then,

m₃a = m₃g – T₂ (1) 

m₂a = T₂ – T_­1 (2) 

m₁a = T₁ – m₁g (3) 

Adding (1) + (2) + (3), we get

a(m₁ + m₂ + m₃) = (m₃ – m₁)g 

a(1 + 6 + 3) = (3 – 1) 10 

10a = 2 × 10 

Thus, the answer is

a = 2 m/s.