JEE Main Physics - Newtons Laws of Motion
Exam Duration: 60 Mins Total Questions : 30
The force of friction
- (a)
is directly proportional to ares of contact between the surfaces for a given load.
- (b)
does not always oppose the relative motion of one surface over another.
- (c)
acts parallel to the instantaneous velocity of a body
- (d)
acts parallel to but opposite in direction to the instaneous velocity of a body.
A coin lying on a meter stic starts to slide when one end of the stick is raised 36.4 cm above the horizontal
- (a)
The limiting angle for friction is \(21^{o}\)
- (b)
The coefficient of starting friction is 0.38
- (c)
both (a) and (b) are correct
- (d)
None of the above
A ball of mass 0.6 kg attached to light inextensible string rotates in a vertical circle of radius 1.2 m, such horizontal. The speed of the ball at the lowest point on its circular path is
- (a)
6.45 \(ms^{-1}\)
- (b)
5 \(ms^{-1}\)
- (c)
2.89 \(ms^{-1}\)
- (d)
7.89 \(ms^{-1}\)
A body of mass 50 kg is pulled by a ro[e of length 6 m on a surface by a force 106 N applied at the other end. The linear density of the rope is 0.5 kg/m. The force acting on 50 kg mass is:
- (a)
50 N
- (b)
100 N
- (c)
150 N
- (d)
200 N
An electric fan is placed on a stationary boat and air is blown with it on the sail of the boat. Which of the following statements is correct?
- (a)
The boat will be uniformly accelerated in the direction of the flow of the air.
- (b)
The boat will start moving with uniform speed.
- (c)
The boat will be uniformly accelerated opposite to the irection of flow of air.
- (d)
The boat will remain stationary as before.
Which of the following statements about the centripetal and centrifigal forces is correct?
- (a)
Centripetal force balances the centrifugal force,
- (b)
both centripetal force and centrifugal force act on the same body
- (c)
centripetal force is directed opposite to the cetrifugal force.
- (d)
centripetal force is expreriened by the observer at the center of the circular path described by the body
Suppose a rocket with an initial mass M0 expels a mass Δm in the form of gases in time Δt, then the mass of the rocket after time t is:
- (a)
M0
- (b)
M0+\(\frac { \triangle m }{ \triangle t } \)
- (c)
M0-\(\frac { \triangle m }{ \triangle t } \)t
If the tension in the cable of 1000 kg elevator is 1000 kg weight, the elevator:
- (a)
is accelerating upwards
- (b)
is accelerating downwards
- (c)
may be at rest or accelerating
- (d)
may be at rest or in uniform motion
Two masses of 8 kg and 4 kg are connected by a string as shown in the figure over a frictionless pulley. The acceleration of the system is:
- (a)
4 ms-2
- (b)
2 ms-2
- (c)
zero
- (d)
9.8 ms-2
The maximum force of static friction upto which body does not move is called:
- (a)
normal reaction
- (b)
coefficient of friction
- (c)
limiting friction
- (d)
rolling friction
Friction:
- (a)
does not affect the efficiency of a machine
- (b)
increases the efficiency of a machine
- (c)
decreases the efficiency of a machine
- (d)
nothing can be said about the effect of friction on efficiency of a machine
The rate of mass of the gas emitted from rear of a rocket is initially 0.1 kg/sec. If the speed of the gas relative to the rocket is 50 m/sec and mass of the rocket is 2 kg, then the acceleration of the rocket (in m/sec2) is:
- (a)
5
- (b)
5.2
- (c)
2.5
- (d)
25
Tyres are inflated to the required value to save fuel. Because of this:
- (a)
normal reaction is increased
- (b)
normal reaction is decreased
- (c)
contact area is increased
- (d)
contact area is decreased
A body is projected upwards with a kinetic energy of 100 J. Taking the friction of air into account, when it returns to the earth, its kinetic energy will be:
- (a)
100 J
- (b)
< 100 J
- (c)
> 100 J
- (d)
none of these
An object is kept on a smooth inclined plane of 1 in I. The horizontal acceleration to be imparted to the inclined plane so that the object is stationary relative to incline is:
- (a)
g\(\sqrt { { l }^{ 2 }-1 } \)
- (b)
g(l2-1)
- (c)
\(\frac { g }{ \sqrt { { l }^{ 2 }-1 } } \)
- (d)
\(\frac { g }{ { l }^{ 2 }-1 } \)
In the first second of its flight, rocket ejects 1/60of its mass with a velocity of 2400 ms-1. The acceleration of the rocket is:
- (a)
19.6 ms-2
- (b)
30.2 ms-2
- (c)
40 ms-2
- (d)
49.8 ms-2
A block of wood resting on an inclined plane of angle 30°, just starts moving down. If the coefficient of friction is 0.2, its velocity (in ms -1) after 5 seconds is: (g = 10 ms -2 )
- (a)
12.75
- (b)
16.34
- (c)
18.25
- (d)
20
A ball of mass 109 moving perpendicular to the plane of the wall strikes it and rebounds in the same line with the same velocity. If the impulse experienced by the wall is 0.54 N s, the velocity of the ball is:
- (a)
27 ms-1
- (b)
3.7 ms-1
- (c)
54 ms-1
- (d)
37 ms-1
- (e)
5.4 ms-1