Top JEE 2021 PYQs on Laws of Motion – With Detailed Solutions

Q1. A particle is projected with velocity Vo along x-axis. A damping force is acting on the particle which is proportional to the square of the distance from the origin i.e, ma = -ax².The distance at which the particle stops : 

Ans :- (d)

Q2. The coefficient of static friction between a wooden block of mass 0.5 kg and a vertical rough wall is 0.2. The magnitude of horizontal force that should be applied on the block to keep it adhere to the wall will be [g = 10 ms-²]  ____N.

Ans.  F=25N

Q3. An inclined plane is bent in such a way that the  vertical cross-section is given by y= x²/4y is in vertical and x in horizontal direction. If the upper surface of this curved plane is rough with coefficient of friction µ = 0.5, the maximum height in cm at which a stationary block will not slip downward is ____cm.

Ans. H=25cm

Q4. Two masses A and B, each of mass M are fixed together by a massless spring. A force acts on the mass B as shown in figure. If the mass A starts moving away from mass B with acceleration 'a', then the acceleration of mass B wil be :

(a) Ma-F/M                 (b) MF/F+Ma
(c)F+Ma/M                  (d) F-Ma/M

Ans.(d)

Q5. A particle is moving with uniform speed along the circumference of a circle of radius R under the action of a central fictitious force F which is inversely proportional to R³. Its time period of revolution will be given by :

Explanation:
Given:
F ∝ 1/R³

In circular motion:
F = mv² / R ⇒ v² ∝ 1/R²

Time period T = 2πR / v ⇒ T ∝ R / v ⇒ T ∝ R × R = R²

∴ T ∝ R²

 ✅ Correct Option: (b)