Laws of Motion

NEET Physics · 100 questions · Page 1 of 10 · Click an option or "Show Solution" to reveal answer

A box of mass 15 kg is on floor of stationary trolley. Coefficient of static friction = 0.12. Maximum acceleration of trolley (g=10 m/s^2):

A 2.1

B 1.8

C 1.5

D 1.2

Correct Answer

Option D

Solution

a = mu*g = 0.12*10 = 1.2 m/s^2

Two perpendicular forces 8N and 6N act on 5 kg mass. Magnitude and direction of acceleration:

A 20 m/s^2; arctan(4/3) with 8N

B 2 m/s^2; arctan(3/4) with 6N

C 2 m/s^2; arctan(4/3) with 8N

D 2 m/s^2; arctan(3/4) with 8N

Correct Answer

Option D

Solution

F_net = sqrt(6^2+8^2) = 10N. a = 10/5 = 2 m/s^2. tan(theta) = 6/8, theta = arctan(3/4) from 8N.

A block of mass 2 kg on rough inclined surface AC with coefficient of friction 1/sqrt(3). Net force on block if g=10 m/s^2:

A 10*sqrt(3)

B zero

C 10

D 20

Correct Answer

Option B

Solution

mu = 1/sqrt(3) = tan(30°). Since mu = tan(theta), block is at rest and net force = 0.

A football player moving southward suddenly turns eastward with same speed. Force on player while turning is:

A along northward

B along north-east

C along south-west

D along eastward

Correct Answer

Option B

Solution

Delta_V = V_final - V_initial = V(east) - V(south) = north-east direction.

Maximum acceleration of car so body lying on floor remains stationary. Coefficient of static friction = 0.15, g = 10 m/s^2:

A 150 m/s^2

B 1.5 m/s^2

C 50 m/s^2

D 1.2 m/s^2

Correct Answer

Option B

Solution

a_max = mu_s * g = 0.15 * 10 = 1.5 m/s^2

A bullet travels 24 cm through a block, velocity reduces to u/3. Total length of block if bullet comes to rest at other end:

A 24 cm

B 28 cm

C 30 cm

D 27 cm

Correct Answer

Option D

Solution

From v^2=u^2+2as: (u/3)^2 = u^2 - 2a*24, so 2ax = 8u^2/9. For total: 2a*x2 = u^2. x/x2 = 8/9, x2 = 27cm.

Two bodies 4 kg and 6 kg tied to ends of string over frictionless pulley. Acceleration in terms of g:

A g/2

B g/5

C g/10

D g

Correct Answer

Option B

Solution

a = (m1-m2)*g/(m1+m2) = (6-4)*g/(6+4) = g/5

A mass m on thin wire whirled in vertical circle. Wire most likely to break when:

A wire is horizontal

B inclined at 60° from vertical

C mass at lowest point

D mass at highest point

Correct Answer

Option C

Solution

T is maximum at lowest point where T - mg*cos(0) = mv^2/R, giving maximum tension.

Block 10 kg inside hollow cylinder radius 1m, friction mu=0.1. Minimum angular velocity to keep block stationary (g=10 m/s^2):

A 10/(2*pi) rad/s

B 10 rad/s

C 10*pi rad/s

D sqrt(10) rad/s

Correct Answer

Option B

Solution

mu*m*r*omega^2 >= mg, omega >= sqrt(g/(mu*r)) = sqrt(10/(0.1*1)) = 10 rad/s

Q10

Which statement is incorrect about friction?

A Rolling friction is smaller than sliding friction.

B Limiting value of static friction is directly proportional to normal reaction.

C Frictional force opposes the relative motion.

D Coefficient of sliding friction has dimensions of length.

Correct Answer

Option D

Solution

F = mu*N gives [mu] = M^0*L^0*T^0, so coefficient of sliding friction is dimensionless.

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