Hi all
What comes to your mind when you think about Newton's first law of motion . Now a days it has become an obvious statement but it was not the case when the law has been formulated. Statement of Newton's first Law of motion is
" Every body continues to be in state of rest or uniform motion untill acted upon by a net external force."
Equilibrium of the bodies is the essence of the forst law of motion.
Why we have used the word net force it is because there might be more then one forces acting on the body and net force on the body is the vector sum of all the forces acting on the body. Newton's first law of motion only gives the qualitative defination of the force that is it tells us that force is only the influence behind the moving objects but it does not tell anything about what is required to keep objects moving when they are set to motion by the application of force. In out daily life we see that bodies set to motion eventualy came to rest for example book placed on a horizontal surface is pushed , it started to move and then come to rest. What does first law of motion has to explain about this effect. What would we have to do to keep the book moving ? Can first law of motion has anything to say about it. Think about it if you find any more point to discuss let me know I'll be happy to discuss
Physics Expert
For complete notes on Newton's Laws of motion visit Newton's Laws of motion
Showing posts with label Newtons Law of motion. Show all posts
Showing posts with label Newtons Law of motion. Show all posts
Saturday, 14 August 2010
Tuesday, 25 May 2010
Newton's Law of Motion (Objective Type Questions)
(1)Friction force can be reduced to great extent by
a. lubricating the two moving parts
b. using ball bearing between two moving parts
c. introducing a thin cushion of air maintained between two relatively moving surfaces
d. all the above
(2) Force exerted on a body can change its
a. kinetic energy
b. direction of motion
c. speed
d. momentum
(3) A block is released from the top of a smooth inclined plane. Another block of same mass is allowed to fall freely from the top of the inclined plane. Both blocks reach the bottom of the plane
a. with equal speed
b. in equal interval of time
c. with equal kinetic energy
d. with equal momentum
(4) Which of the following expression does not represent the force acting on the body of mass m
a. GMem/(Re)2
b. ma
c. μN
d. 6ηπrv
(5) A body of mass m is resting on the floor. A minimum amount of force is applies on the body and the force continues to act on the body as it moves. If coefficent of static and dynamic friction are 0.4 and 0.3 resp. then the acceleration of the body is
a. 0
b. 3.98
c. 0.98
d. 4.98
Answer
(1) d.
(2) a, b, c, d
(3) a and c
(4) d
(5) c
you can discuss these questions with me by becoming a member of my group physicsgoeasy
I'll be happy to help.
a. lubricating the two moving parts
b. using ball bearing between two moving parts
c. introducing a thin cushion of air maintained between two relatively moving surfaces
d. all the above
(2) Force exerted on a body can change its
a. kinetic energy
b. direction of motion
c. speed
d. momentum
(3) A block is released from the top of a smooth inclined plane. Another block of same mass is allowed to fall freely from the top of the inclined plane. Both blocks reach the bottom of the plane
a. with equal speed
b. in equal interval of time
c. with equal kinetic energy
d. with equal momentum
(4) Which of the following expression does not represent the force acting on the body of mass m
a. GMem/(Re)2
b. ma
c. μN
d. 6ηπrv
(5) A body of mass m is resting on the floor. A minimum amount of force is applies on the body and the force continues to act on the body as it moves. If coefficent of static and dynamic friction are 0.4 and 0.3 resp. then the acceleration of the body is
a. 0
b. 3.98
c. 0.98
d. 4.98
Answer
(1) d.
(2) a, b, c, d
(3) a and c
(4) d
(5) c
you can discuss these questions with me by becoming a member of my group physicsgoeasy
I'll be happy to help.
Sunday, 21 March 2010
String, pully and spring
A lot of problems in mechanics involves string, pulley and springs for example masses are attached to string or spring and so on. Here are some concepts you need to remember while solving problems involving string, spring and pulleys.
(1) String
A. If not staded in the question consider the string to be inextensible.
B. Different blocks connected to an inextensible string would have same acceleration and for extensible string blocks would have different acceleration until the string can stretch.
C. Unless otherwise specified consider the string to be light i.e., consider its mass to be negligible in comparison to the block connected to it.
D. For a massless string tension in the string is zero although an ideal massless string is an practical impossibility.
E. Tension on different parts of the string would be different if string possess a considerable mass.
(2) Pulley
A. Unless or otherwise specified consider the pulley to be light having no effect on the system due to its weight.
B. The tension on strion on either side of pulley is taken to be same
C. If not specified consider the oulley to be frictionless in nature.
(3) Spring
A. Unless or otherwise specified consider the spring to be light and force constant of spring is same throughout whole length of the spring.
B. Spring has a elastic property that it can be compressed and stretched easily.
C. To stretch or compress a spring equal and opposite forces have to be applied at both the ends of the spring and in responce spring apply equal and opposite restoring force to bring the spring back to its natural position.
D For small compression and elongations this restoring force is given by Hook's Law which is
F=kx
where k is the spring constant and x is elongation or compression from the natural length of the spring.
So keep solving more and more physics problems Keeping these facts in mind. All the very best for your exams.
(1) String
A. If not staded in the question consider the string to be inextensible.
B. Different blocks connected to an inextensible string would have same acceleration and for extensible string blocks would have different acceleration until the string can stretch.
C. Unless otherwise specified consider the string to be light i.e., consider its mass to be negligible in comparison to the block connected to it.
D. For a massless string tension in the string is zero although an ideal massless string is an practical impossibility.
E. Tension on different parts of the string would be different if string possess a considerable mass.
(2) Pulley
A. Unless or otherwise specified consider the pulley to be light having no effect on the system due to its weight.
B. The tension on strion on either side of pulley is taken to be same
C. If not specified consider the oulley to be frictionless in nature.
(3) Spring
A. Unless or otherwise specified consider the spring to be light and force constant of spring is same throughout whole length of the spring.
B. Spring has a elastic property that it can be compressed and stretched easily.
C. To stretch or compress a spring equal and opposite forces have to be applied at both the ends of the spring and in responce spring apply equal and opposite restoring force to bring the spring back to its natural position.
D For small compression and elongations this restoring force is given by Hook's Law which is
F=kx
where k is the spring constant and x is elongation or compression from the natural length of the spring.
So keep solving more and more physics problems Keeping these facts in mind. All the very best for your exams.
Monday, 17 March 2008
Conceptual question for Newton's law
1. when a Force is exerted on a body ,it can change
(a) Direction of motion
(b) Momentum
(c) Kinetic energy
(d) All the above
2. there are two statements
A Rate of change of momentum correspondes to force
B Rate of change of momentum corresponds to Kinetic Energy
Which of the following is correct
(a) A only
(b) B only
(c) Both A and B are correct
(d) Both A and B are wrong
3. A truck and car are moving on a plane road with same kinetic Energy. They are brought to rest by application of brakes which provide equal retarding forces. Which of the following statements is true.
(a) Distance travelled by truck is shorter then car before comming to rest
(b) Distance travelled by car is shorter then truck before comming to rest
(c) Distance travelled depends on individual velocity of both the vehicles
(d) Both will travel same distance before comming to rest
4. A block A of mass m1 is released from top of smooth inclined plane and it slides down the plane. Another block of mass m2 such that m2 > m1 is dropped from the same point and falls vertically downwards. Which one of the following statements will be true if the friction offered by air is negligible?
(a) Both blocks will reach ground at same time
(b) Both blocks will reach ground with the same speed
(c) speed of both the blocks when they reach ground will depend on their masses
(d) Block A reaches ground brfore block B
5. Which of the following observer is/are non interial
a.A child revolving in the merry ground
b. A driver in a train moving with constant velocity v
c. A passenger in a bus which is slowing down to a stop
d None of these
6. there are two statements
A Newtons first law in valid from the pilot in an aircraft which is taking off
B Newtons first law in valid from the observer in a train moving with constant velocity
Which of the following is correct
(a) A only
(b) B only
(c) Both A and B are correct
(d) Both A and B are wrong
7.A IITJEE text book of mass M rests flat on a horizontal table of mass m placed on the ground.Let RX->Y be the constant force exerted by the body x on body Y.According to Newton third law,which of the following is an action-reaction pair of forces?
a. (M+m)g and Rtable->book
b. Rground->table and mg+Rbook->table
c. Rground->table and Rtable->ground
d Mg and Rtable->book
8. Choose the correct alternative
a. The acceleration of a moving particle is always in the direction of its velocity
b. Velocity and acceleraion vectors of a moving particle may have any angle between 0 and 360 between them
c.Velocity and acceleraion vectors of a moving particle may have any angle between 0 and 180 between them
d. If the acceleration vector is always perpendicular to the velocity vector of a moving particle,the velocity vector does not change
Solutions
Detailed Solutions
Ans 1:
A body acted uopn by a certain force produces acceleration i.e. it undergoes change in it's velocity. hence choice (d) is correct
Ans 4.
since velocity of block when it reaches the ground is given by v=(2gh)1/2 and it is independent of the mass the correct choice will be (b).
Ans 6
We know that Newtons law is invalid in Non interial frame of refrence, now since acceleration is present in Ist case..So answer is B
Ans 7.
Action reaction pair acts on diffrent body and always are in oppsite direction.We will have to draw free body diagram for each part in this case.
(a) Direction of motion
(b) Momentum
(c) Kinetic energy
(d) All the above
2. there are two statements
A Rate of change of momentum correspondes to force
B Rate of change of momentum corresponds to Kinetic Energy
Which of the following is correct
(a) A only
(b) B only
(c) Both A and B are correct
(d) Both A and B are wrong
3. A truck and car are moving on a plane road with same kinetic Energy. They are brought to rest by application of brakes which provide equal retarding forces. Which of the following statements is true.
(a) Distance travelled by truck is shorter then car before comming to rest
(b) Distance travelled by car is shorter then truck before comming to rest
(c) Distance travelled depends on individual velocity of both the vehicles
(d) Both will travel same distance before comming to rest
4. A block A of mass m1 is released from top of smooth inclined plane and it slides down the plane. Another block of mass m2 such that m2 > m1 is dropped from the same point and falls vertically downwards. Which one of the following statements will be true if the friction offered by air is negligible?
(a) Both blocks will reach ground at same time
(b) Both blocks will reach ground with the same speed
(c) speed of both the blocks when they reach ground will depend on their masses
(d) Block A reaches ground brfore block B
5. Which of the following observer is/are non interial
a.A child revolving in the merry ground
b. A driver in a train moving with constant velocity v
c. A passenger in a bus which is slowing down to a stop
d None of these
6. there are two statements
A Newtons first law in valid from the pilot in an aircraft which is taking off
B Newtons first law in valid from the observer in a train moving with constant velocity
Which of the following is correct
(a) A only
(b) B only
(c) Both A and B are correct
(d) Both A and B are wrong
7.A IITJEE text book of mass M rests flat on a horizontal table of mass m placed on the ground.Let RX->Y be the constant force exerted by the body x on body Y.According to Newton third law,which of the following is an action-reaction pair of forces?
a. (M+m)g and Rtable->book
b. Rground->table and mg+Rbook->table
c. Rground->table and Rtable->ground
d Mg and Rtable->book
8. Choose the correct alternative
a. The acceleration of a moving particle is always in the direction of its velocity
b. Velocity and acceleraion vectors of a moving particle may have any angle between 0 and 360 between them
c.Velocity and acceleraion vectors of a moving particle may have any angle between 0 and 180 between them
d. If the acceleration vector is always perpendicular to the velocity vector of a moving particle,the velocity vector does not change
Solutions
Detailed Solutions
Ans 1:
A body acted uopn by a certain force produces acceleration i.e. it undergoes change in it's velocity. hence choice (d) is correct
Ans 4.
since velocity of block when it reaches the ground is given by v=(2gh)1/2 and it is independent of the mass the correct choice will be (b).
Ans 6
We know that Newtons law is invalid in Non interial frame of refrence, now since acceleration is present in Ist case..So answer is B
Ans 7.
Action reaction pair acts on diffrent body and always are in oppsite direction.We will have to draw free body diagram for each part in this case.
Sunday, 16 March 2008
Newtons law of Motion
Basic concepts of laws of motion
(1) Newton's first law of motion:-
'A body continues to be in state of rest or uniform motion unless it is acted upon by some external force to act otherwise'
(2) Newton's second law of motion:-
'Rate of change of momentum of a body is proportional to the applied force and takes place in the direction of action of force applied'
Mathematically,
F=dp/dt
=ma
where, F=external force applied
p=mv,momentum of the body
a=acceleration
SI unit of force is Newton (N).
(3) Impulse is the product of force and time which is equal to the change in momentum
Impulse=FΔt
=Δp
(4) Newton's third law of motion:-
'To every action there is always an equal and opposite reaction'
FAB=-FBA
(5) According to the law of conservation of linear momentum
Initial momentum = final momentum
m1v1+m2v2=m1v1'+m2v2'
For equilibrium of a body
F1+F2+F3=0
Some points to note
1. An accelerated frame is called non interial frame while am non accelerated frame is called interial frame
2. Newton Ist law are valid in intertial frame only
3 Apparent weight of a body in the lift
Going Upward with acceleration a
W=m(g+a)
Going Down with acceleration a
W=m(g-a)
4.Always draw free body diagram to solve the force related problems
(1) Newton's first law of motion:-
'A body continues to be in state of rest or uniform motion unless it is acted upon by some external force to act otherwise'
(2) Newton's second law of motion:-
'Rate of change of momentum of a body is proportional to the applied force and takes place in the direction of action of force applied'
Mathematically,
F=dp/dt
=ma
where, F=external force applied
p=mv,momentum of the body
a=acceleration
SI unit of force is Newton (N).
(3) Impulse is the product of force and time which is equal to the change in momentum
Impulse=FΔt
=Δp
(4) Newton's third law of motion:-
'To every action there is always an equal and opposite reaction'
FAB=-FBA
(5) According to the law of conservation of linear momentum
Initial momentum = final momentum
m1v1+m2v2=m1v1'+m2v2'
For equilibrium of a body
F1+F2+F3=0
Some points to note
1. An accelerated frame is called non interial frame while am non accelerated frame is called interial frame
2. Newton Ist law are valid in intertial frame only
3 Apparent weight of a body in the lift
Going Upward with acceleration a
W=m(g+a)
Going Down with acceleration a
W=m(g-a)
4.Always draw free body diagram to solve the force related problems
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