Physics - Newtons Laws of Motion
Exam Duration: 45 Mins Total Questions : 30
A train is moving at a constant speed along a straight level track. Then
- (a)
the frictional force is zero
- (b)
the frictional force on the engine and the coach acts in the same direction
- (c)
the pushing force is greater than the frictional force
- (d)
the resultant of all the forces acting on the train is zero
Two balls of masses \(m_{1}\) and \(m_{2}\) are separated from each other by a powder charge placed between them. The whole system is at rent on the ground. Suddenly, the powder charge explodes and masses are pushed apart. The mass \(m_{1}\)travels a distance \(s_{1}\) and stops. If the coefficients of friction between balls and ground are same, mass \(m_{2}\) stops after travelling distance
- (a)
\(s_{2}={m_{1}\over m_{2}}s_{1}\)
- (b)
\(s_{2}={m_{2}\over m_{1}}s_{1}\)
- (c)
\(s_{2}={m_{1}\over m_{2}^{2}}s_{1}\)
- (d)
\(s_{2}={m_{2}^{2}\over m^{2}_{1}}s_{1}\)
A 15 kg mass is accelerated from rest with a force of 100N. As it moves faster, friction and air resistance create an oppositely directed reatarding force given by \(F_{R}=A+B\vartheta \)
Where A=25 N and B=0.5 N/ms. At what velocity does the acceleration equal to one half of the initial acceleration ?
- (a)
25 \(ms^{-1}\)
- (b)
50 \(ms^{-1}\)
- (c)
75 \(ms^{-1}\)
- (d)
100 \(ms^{-1}\)
A black slides with a velocity of 10\(ms^{-1}\) on a rough horizontal surface. It comes to rest after covering a distance of 50 m. If g is 10 \(ms^{-2}\), then coefficient of dynamic friction between the block and surface is
- (a)
1
- (b)
10
- (c)
0.2
- (d)
0.1
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.
The limiting friction is:
- (a)
always greater than the dynamic friction
- (b)
always less than the dynamic friction
- (c)
equal to the dynamic friction
- (d)
sometimes greater and sometimes less than the dynamic friction
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
A truck, weighing 8000 kg, is moving along a track with negligible friction at 1.8 ms -1 with the engine turn off when it begins to rain hard. The raindrops fall vertically with respect to the ground. The speed of the truck, when it has collected 1000 kg of rain water, is:
- (a)
1.6 ms-1
- (b)
10 ms-1
- (c)
3 ms-1
- (d)
9 ms-1
Assuming the gravity to be in negative Z-direction, a force \(\vec { F } =\vec { v } \times \vec { A } \) is exerted on a particle in addition to the force of gravity, where \(\vec { v } \) is the velocity and \(\vec { A} \) is a constant vector in positive X -direction. With what minimum speed a particle of mass m be projected so that it continues to move undeflected with constant velocity?
- (a)
-\(\frac { A }{ mg } \hat { j } \)
- (b)
\(\frac { A }{ mg } \hat { j } \)
- (c)
\(\frac { mg }{ A } \hat { j } \)
- (d)
-\(\frac { mg }{ A } \hat { j } \)
What should be the maximum mass M2, so that block M1 slides downwards in above question?
- (a)
M2=M1(sinθ+μcosθ
- (b)
M2=M1(sinθ-μcosθ)
- (c)
M2=\(\frac { { M }_{ 1 } }{ sin\theta +\mu cos\theta } \)
- (d)
M2=\(\frac { { M }_{ 1 } }{ sin\theta -\mu cos\theta } \)
Consider a car moving along a straight horizontal road with a speed of 72 km/h. If the coefficient of static friction between the tyre and the road is 0.5, the shortest distance in which the car can be stopped is: (Take g = 10m s-2)
- (a)
30 m
- (b)
40 m
- (c)
72 m
- (d)
20 m
A body is moving with uniform velocity of 2 ms-1 on a rough level surface. The frictional force on it is 10 N. If the body moves with velocity 4 ms-1 the force of friction will be:
- (a)
2.5 N
- (b)
5 N
- (c)
10 N
- (d)
20 N
A body is rolling on the ground with a velocity of 1 m/s. After travelling a distance of 5 m, the body stops. The coefficient of friction is:
- (a)
0.00102
- (b)
0.0102
- (c)
0.102
- (d)
1.02
An ice cart of mass 60 kg rests on a horizontal snow patch with coefficient of static friction \(\frac{1}{3}\) Assuming that there is no vertical acceleration, find the magnitude of the maximum horizontal force required to move the ice cart: (Take g=9.8 ms-2)
- (a)
100 N
- (b)
110 N
- (c)
209 N
- (d)
196 N
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)
\(\frac { g }{ { l }^{ 2 }-1 } \)
A bullet comes out of the barrel of a gun of length 2 m with a speed of 80 m/s. The average acceleration of the bullet is:
- (a)
1.6 m/s2
- (b)
160 m/s2
- (c)
1600 m/s2
- (d)
16 m/s2
A block of base 10 cm x 10 cm and height 15 cm is kept on an inclined plane. The coefficient of friction between them is \(\sqrt{3}\) . The inclination θ of this inclined plane from the horizontal plane is gradually increased from 0°. Then:
- (a)
at θ = 300, the block will start sliding down the plane
- (b)
the block will remain at rest on the plane upto certain θ and then it will topple
- (c)
at θ = 600, the block will start sliding down the plane and continue to do so at higher angles
- (d)
at θ = 600, the block will start sliding down the plane and on further increasing θ, it will topple at certain θ