Laws of Motion & Friction · JEE Main previous year questions

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2021 23 questions

Q342021 · 1 Sept 2021 · Shift 2
A body of mass 'm' dropped from a height 'h' reaches the ground with a speed of $0.8 g h$ . The value of work done by the air-friction is :
1. A. $- 0.68 mgh$
2. B. $mgh$
3. C. $1.64 mgh$
4. D. $0.64 mgh$
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Answer: A
Q362021 · 1 Sept 2021 · Shift 2
1. A. $\frac{4}{3} g$
2. B. $\frac{6}{5} g$
3. C. $\frac{3}{5} g$
4. D. $\frac{2}{3} g$
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Answer: D
Q442021 · 1 Sept 2021 · Shift 2
1. A.
2. B.
3. C.
4. D.
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Answer: C
Q542021 · 1 Sept 2021 · Shift 2· Numerical answer
When a body slides down from rest along a smooth inclined plane making an angle of $3 0^{\circ}$ with the horizontal, it takes time T. When the same body slides down from the rest along a rough inclined plane making the same angle and through the same distance, it takes time $α T$ , where $α$ is a constant greater than 1. The co-efficient of friction between the body and the rough plane is $\frac{1}{x} (\frac{α ^{2} - 1}{α ^{2}})$ where x = ____.
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Answer: 3
Q472021 · 26 Aug 2021 · Shift 2
1. A. $125 cm$
2. B. $1250 cm$
3. C. $12.5 cm$
4. D. $1.25 cm$
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Answer: C
Q512021 · 26 Aug 2021 · Shift 2· Numerical answer
Two waves are simultaneously passing through a string and their equations are : $y_{1} = A_{1} sin k (x - v t)$ , $y_{2} = A_{2} sin k (x - v t + x_{0})$ . Given amplitudes $A_{1} = 12 mm$ and $A_{2} = 5 mm$ , $x_{0} = 3.5 cm$ and wave number $k = 6.28 cm^{- 1}$ . The amplitude of resulting wave will be ............... mm.
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Answer: 7
Q602021 · 26 Aug 2021 · Shift 2· Numerical answer
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Answer: 15
Q572021 · 27 Jul 2021 · Shift 2· Numerical answer
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Answer: 2
Q412021 · 25 Jul 2021 · Shift 1
1. A.1 : 1
2. B. $2 : 1$
3. C.2 : 1
4. D. $1 : 2$
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Answer: B
Q552021 · 25 Jul 2021 · Shift 1· Numerical answer
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Answer: 10
Q342021 · 22 Jul 2021 · Shift 2
A porter lifts a heavy suitcase of mass $80 kg$ and at the destination lowers it down by a distance of $80 cm$ with a constant velocity. Calculate the work done by the porter in lowering the suitcase. (take $g = 9.8 ms^{- 2}$ )
1. A. $+ 627.2 J$
2. B. $- 62720.0 J$
3. C. $- 627.2 J$
4. D. $784.0 J$
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Answer: C
Q402021 · 22 Jul 2021 · Shift 2
A bullet of ' $4 g$ ' mass is fired from a gun of mass $4 kg$ . If the bullet moves with the muzzle speed of $50 ms^{- 1}$ , the impulse imparted to the gun and velocity of recoil of gun are :
1. A. $0.2 kg ms^{- 1}, 0.1 ms^{- 1}$
2. B. $0.4 kg ms^{- 1}, 0.05 ms^{- 1}$
3. C. $0.2 kg ms^{- 1}, 0.05 ms^{- 1}$
4. D. $0.4 kg ms^{- 1}, 0.1 ms^{- 1}$
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Answer: C
Q542021 · 20 Jul 2021 · Shift 1· Numerical answer
A circular disc reaches from top to bottom of an inclined plane of length 'L'. When it slips down the plane, it makes time ' $t_{1}$ '. When it rolls down the plane, it takes time $t_{2}$ . The value of $\frac{t _{2}}{t _{1}}$ is $\frac{3}{x}$ . The value of x will be ________.
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Answer: 2
Q572021 · 20 Jul 2021 · Shift 1· Numerical answer
A rod of mass M and length L is lying on a horizontal frictionless surface. A particle of mass 'm' travelling along the surface hits at one end of the rod with a velocity 'u' in a direction perpendicular to the rod. The collision is completely elastic. After collision, particle comes to rest. The ratio of masses $(\frac{m}{M})$ is $\frac{1}{x}$ . The value of 'x' will be ________.
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Answer: 4
Q422021 · 18 Mar 2021 · Shift 2
1. A.0
2. B. $5 m g$
3. C. $\frac{7}{2} m g$
4. D. $\frac{m g}{5}$
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Answer: D
Q332021 · 16 Mar 2021 · Shift 1
1. A. $\frac{F}{m} cos θ + μ_{k} (g - \frac{F}{m} sin θ)$
2. B. $\frac{F}{m} cos θ - μ_{k} (g - \frac{F}{m} sin θ)$
3. C. $- \frac{F}{m} cos θ - μ_{k} (g - \frac{F}{m} sin θ)$
4. D. $\frac{F}{m} cos θ - μ_{k} (g + \frac{F}{m} sin θ)$
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Answer: B
Q542021 · 16 Mar 2021 · Shift 1· Numerical answer
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Answer: 20
Q512021 · 26 Feb 2021 · Shift 1· Numerical answer
A person standing on a spring balance inside a stationary lift measures 60 kg. The weight of that person if the lift descends with uniform downward acceleration of $1.8 m/ s^{2}$ will be _________ N. $[g = 10 m/ s^{2}]$
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Answer: 492
Q582021 · 26 Feb 2021 · Shift 1· Numerical answer
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Answer: 3.33
Q332021 · 25 Feb 2021 · Shift 2
1. A. $\frac{v _{0}^{2}}{2 g s i n θ}$
2. B. $\frac{7 v _{0}^{2}}{10 g s i n θ}$
3. C. $\frac{2}{5} \frac{v _{0}^{2}}{g s i n θ}$
4. D. $\frac{v _{0}^{2}}{5 g s i n θ}$
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Answer: B
Q522021 · 25 Feb 2021 · Shift 2· Numerical answer
The percentage increase in the speed of transverse waves produced in a stretched string if the tension is increased by 4%, will be __________%.
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Answer: 2
Q552021 · 25 Feb 2021 · Shift 2· Numerical answer
Two identical conducting spheres with negligible volume have 2.1 nC and $- 0.1 nC$ charges, respectively. They are brought into contact and then separated by a distance of 0.5 m. The electrostatic force acting between the spheres is ______ $\times 1 0^{- 9} N$ . $[Given : 4 π ε_{0} = \frac{1}{9 \times 1 0 ^{9}} SI unit]$
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Answer: 36
Q582021 · 25 Feb 2021 · Shift 2· Numerical answer
Two particles having masses 4 g and 16 g respectively are moving with equal kinetic energies. The ratio of the magnitudes of their linear momentum is n : 2. The value of n will be ___________.
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Answer: 1