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A few numerical problems from laws of motion

  1. A worker pulls a 200. N packing crate with an applied force of 55.0 N.  The crate accelerates at a rate of 0.250  m/s(squared).  What is the coefficient of kinetic friction between the crate and the factory floor?
  2. A student pulls a 150. N sled up a 28 degree slope at a constant speed by applying a force of 100. N.  Near the top of the hill he releases the sled.  With what acceleration does the sled go down the hill?
  3. A 200. N crate rests on a ramp; the maximum angle just before it slips is 25 degrees with the horizontal.  What is the coefficient of static friction between the crate and the surface of the ramp?
  4. A man pulls a sled with a weight of 200. N with a constant velocity across a horizontal snow surface.  If a force of 80N is being applied to the sled rope at an angle of 53 degrees to the ground, what is the coefficient of friction between the sled and the ground?
  5. A jet plane is flying with  a constant speed along a straight line at an angle of 30degree  above the horizontal. The weight of plane is 86 500N. Its engine provides a forward thrust T of 103 000N. The lift of force L(directed perpendicular to the wings)and the force R of air resistance (directed opposite to the motion)act on the plane. Find L & R

Which books should be referred for IIT JEE ?

We have received hundreds of questions on the above subject. As the questions continue to pour in, we found it necessary to create a post on it.

IIT JEE is an entrance exam of international repute and IITs are considered at par with MIT by many. So, if you are an IIT aspirant, it is very much essential to prepare well in advance.

In this article we are focusing on Physics only

Know the fundamentals

Knowing the fundamentals is the first step. Learn your daily lessons well. In learning Physics, “Questioning Every Answer is more important than Answering Every Question”

Whenever you learn a new concept, try to get all the doubts clarified. Ask doubts and questions to your teachers. (If they don’t answer you satisfactorily, post them at www.askphysics.com )

Observe your surrounding and try finding examples on what you have learnt. The syllabus and books give you a framework on what to study; but don’t just limit your studies on books and syllabus. Search related information from real life and other sources of reference.

RECOMMENDED BOOKS FOR IIT JEE PREPARATION

The very first book you cannot avoid is the NCERT TEXT BOOK for class XI and XII

These books are designed after thorough research and the exercises are carefully added. Be sure to solve all the exercises including the Additional Exercises

Here are some of the Books you can refer for practicing for IIT JEE

  1. Concepts of Physics (by H C Verma)
  2. Fundamentals of Physics (by Resnick, Hallidey)
  3. University Physics (Zemansky)
  4. Problems in Physics (IE Irodov)

 

By the by, having too much books will be a hindrance. It is better to start with the NCERT books and after mastering all the exercises take up Resnick Hallidey and after clarifying the concepts take up Problems from H C Verma’s concepts of Physics and then go on to IRODOV if time allows.

Wish you all the best.

Pseudo force and solving problems

Sir,can we solve problem without considering pseudo forces in non inertial frame?(give an example)

Solving problems on Laws of Motion

Sir,in solving problems of laws of motion ,is it mandatory to take that direction as +ve in which acceleration acts?(i.e should i subtract other forces acting on a body from the forces that is acting towards the acceleration)

 

(Pranay Talukdar asks)

Answer: In general, we take the forces in the direction of acceleration (I.E, ENHANCING THE ACCELERATION) and the forces against the acceleration as negative.

The first step in solving such problems is to draw a free body diagram and represent all active forces and reactions to constraints in vector form with proper direction ad label. This will highly simplify the problem.

Numerical Problems from Kinematics and Force

1.if a man in a boat rows perpendicular to the bank he is drifted 120 m during crossing river in 10 minutes . if he heads at angle of alpha from upstream he crosses river by shortest path in 12.5 min.
find width of river,velocity of river with respect to water,velocity of boat with respect to river

2.a projectile is thrown horizontally from top of building of height 10 m with a certain speed u.at same time another projectile thrown from ground 10 m away from building with equal speed u in same vertical plane at angle theta with horizontal.if they collide after 1 second then find u and angle of projections of 1st and 2nd particle

3.a 10 kg block is resting on a rough surface .when force is applied to it for 4s. the variation of force with time is given as (f=100N for 4s.). also (coefficient of friction=0.5) find velocity at t=1s and t=4s.

4. a particle moves in straight line whose acceleration depends on velocity as a=-alpha root v, alpha =+ve constant . at initial moment velocity of particle is Vo.if average speed before it stops is Vo/x find value of x.
(Gireedhar asked these questions)

Answers will be posted soon

Problems from Kinematics again!

  1. Two bodies one held 40 m above other, are released simultaneously . After falling for 3 sec under gravity,  their relative separation is?
  2. A particle covers half the distance between two points for equal time for
    V1 and V2 and other half with V3 and V4 for equal distance. find average
    velocity?

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