Q276
Errorless
6. Self Evaluation Test
MCQ
A block can slide on a smooth inclined plane of inclination $\theta$ kept on the floor of a lift. When the lift is descending with a retardation $a$ , the acceleration of the block relative to the incline is
A.
$(g + a)\sin \theta$
B.
$(g - a)$
C.
$g\sin \theta$
D.
$(g - a)\sin \theta$
Q277
Errorless
6. Self Evaluation Test
MCQ
A $60\mathrm{kg}$ man stands on a spring scale in the lift. At some instant he finds, scale reading has changed from $60\mathrm{kg}$ to $50\mathrm{kg}$ for a while and then comes back to the original mark. What should we conclude
A.
The lift was in constant motion upwards
B.
The lift was in constant motion downwards
C.
The lift while in constant motion upwards, is stopped suddenly
D.
The lift while in constant motion downwards, is suddenly stopped
Q278
Errorless
6. Self Evaluation Test
MCQ
Three weight $A, B$ and $C$ are connected by string as shown in the figure. The system moves over a frictionless pulley. The tension in the string connecting $A$ and $B$ is (where $g$ is
A.
g
B.
$\frac{g}{9}$
C.
$\frac{8g}{9}$
D.
$\frac{10g}{9}$
Q279
Errorless
6. Self Evaluation Test
MCQ
The masses of 10 kg and 20 kg respectively are connected by a massless spring as shown in figure. A force of 200 N acts on the 20 kg mass. At the instant shown, the 10 kg mass has acceleration $12 \, m/sec^{2}$ . What is the acceleration of 20 kg mass
A.
$12m / \sec^2$
B.
$4m / \sec^2$
C.
$10m / \sec^2$
D.
Zero
Q280
Errorless
6. Self Evaluation Test
MCQ
A spring balance and a physical balance are kept in a lift. In these balances equal masses are placed. If now the lift starts moving upwards with constant acceleration, then
A.
The reading of spring balance will increase and the equilibrium position of the physical balance will disturb
B.
The reading of spring balance will remain unchanged and physical balance will remain in equilibrium
C.
The reading of spring balance will decrease and physical balance will remain in equilibrium
D.
The reading of spring balance will increase and the physical balance will remain in equilibrium
Q281
Errorless
1. Static and limiting friction
MCQ
A system consists of three masses $m_{1}$ , $m_{2}$ and $m_{3}$ connected by a string passing over a pulley P. The mass $m_{1}$ hangs freely and $m_{2}$ and $m_{3}$ are on a rough horizontal table (the coefficient of friction = $\mu$ ). The pulley is frictionless and of negligible mass. The downward acceleration of mass $m_{1}$ is
(Assume $m_{1} = m_{2} = m_{3} = m$ )
A.
$g(1 - 2\mu) / 3$
B.
$g(1 - 2\mu) / 2$
C.
$g(1 - g\mu) / 9$
D.
$2g\mu /3$
Q282
Errorless
1. Static and limiting friction
MCQ
Work done by a frictional force is
A.
Negative
B.
Positive
C.
Zero
D.
All of the above
Q283
Errorless
14. Critical Thinking-Friction
MCQ
The time taken by an object to slide down $45^{\circ}$ rough inclined plane is n times as it takes to slide down a perfectly smooth $45^{\circ}$ incline place. The coefficient of kinetic friction between the object and the incline plane is
A.
$\sqrt{\frac{1}{1-n^{2}}}$
B.
$\sqrt{1-\frac{1}{n^{2}}}$
C.
$1+\frac{1}{n^{2}}$
D.
$1-\frac{1}{n^{2}}$
Q284
Errorless
14. Critical Thinking-Friction
MCQ
Calculate the maximum acceleration of a moving car so that a body lying on the floor of the car remains stationary. The coefficient of static friction between the body and the floor is $0.15(g = 10 \, m \, s^{-2})$
A.
$150 \, m \, s^{-2}$
B.
$1.5 \, m \, s^{-2}$
C.
$50 \, m \, s^{-2}$
D.
$1.2 \, m \, s^{-2}$
Q285
Errorless
16. Self Evaluation Test-Friction
MCQ
A force of 19.6 N when applied parallel to the surface just moves a body of mass 10 kg kept on a horizontal surface. If a 5 kg mass is kept on the first mass, the force applied parallel to the surface to just move the combined body is
A.
29.4 N
B.
39.2 N
C.
18.6 N
D.
42.6 N
Q286
Errorless
16. Self Evaluation Test-Friction
MCQ
If the normal force is doubled, the coefficient of friction is
A.
Not changed
B.
Halved
C.
Doubled
D.
Tripled
Q287
Errorless
16. Self Evaluation Test-Friction
MCQ
A body of weight 50 N placed on a horizontal surface is just moved by a force of 28.2 N. The frictional force and the normal reaction are
A.
10N, 15N
B.
20N, 30N
C.
2N, 3N
D.
5N, 6N
Q288
Errorless
16. Self Evaluation Test-Friction
MCQ
A rough vertical board has an acceleration 'a' so that a 2 kg block pressing against it does not fall. The coefficient of friction between the block and the board should be
A.
$ > g / a$
B.
$ < g / a$
C.
= g/a
D.
$>a / g$
Q289
Errorless
16. Self Evaluation Test-Friction
MCQ
A stone weighing 1 kg and sliding on ice with a velocity of 2 m/s is stopped by friction in 10 sec. The force of friction (assuming it to be constant) will be
A.
-20 N
B.
-0.2 N
C.
0.2 N
D.
20 N
Q290
Errorless
16. Self Evaluation Test-Friction
MCQ
A body of mass 10 kg slides along a rough horizontal surface. The coefficient of friction is $1/\sqrt{3}$ . Taking $g = 10 \, m/s^{2}$ , the least force which acts at an angle of $30^{\circ}$ to the horizontal is
A.
25 N
B.
100 N
C.
50 N
D.
$\frac{50}{\sqrt{3}}N$
Q291
Errorless
16. Self Evaluation Test-Friction
MCQ
A child weighing 25 kg slides down a rope hanging from the branch of a tall tree. If the force of friction acting against him is 2 N, what is the acceleration of the child (Take $g = 9.8 \, m/s^{2}$ )
A.
$22.5 \, m/s^{2}$
B.
$8 \, m/s^{2}$
C.
$5 \, m/s^{2}$
D.
$9.72 \, m/s^{2}$
Q292
Errorless
16. Self Evaluation Test-Friction
MCQ
In the above question, if the lift is moving upwards with a uniform velocity, then the frictional resistance offered by the body is
A.
$Mg$
B.
$\mu Mg$
C.
$2\mu Mg$
D.
Zero
Q293
Errorless
16. Self Evaluation Test-Friction
MCQ
A body of mass 2 kg is moving on the ground comes to rest after some time. The coefficient of kinetic friction between the body and the ground is 0.2. The retardation in the body is
A.
$9.8 \, m/s^{2}$
B.
$4.73 \, m/s^{2}$
C.
$2.16 \, m/s^{2}$
D.
$1.96 \, m/s^{2}$