Laws of Motion

IIT JEE -Physics:

IIT JEE -Physics Work, Power, and Energy

SECTION – I:

SECTION – I OBJECTIVE QUESTIONS Only one option is correct

Problem:

01 A ship of mass 3x10 7 kg initially at rest, is pulled by a force of 5x10 4 N through a distance of 3 m. assuming that the resistance due to water is negligible, the speed of the ship is: 1.5m/s 60 m/s 0.1 m/s 5 m/s Problem 1980

Problem:

02 A block of mass 2 kg rests on a rough inclined plane making an angle of 30 0 with the horizontal. The coefficient of static friction between the block and the plane is 0.7. the frictional force on the block is : 9.8N 0.7x9.8x√3N 9.8x √3N 0.7x9.8N Problem 1980

Problem:

03 During paddling of a bicycle, the force of friction exerted by the ground on the two wheels is such that it acts. In the backward direction on the front wheel and in the forward direction on the wear wheel In the forward direction on the front wheel and in the backward direction on the rear wheel In the backward direction on both the front and the rear wheels In the forward direction on both the front and the rear wheels Problem 1990

Problem:

04 A car is moving in a circular horizontal track of radius 10 m with a constant speed of 10 m/s. a plumb bob is suspended from the roof of the car by a light rigid rod. The angle made by the rod with the track is (g=10m/s 2 ): Zero 30 0 45 0 60 0 Problem 1992

Problem:

05 A block of mass 0.1 kg is held against a wall applying a horizontal force of 5 N on the block. If the coefficient of friction between the block and the well is 0.5, the magnitude of the frictional force acting on the block is : 2.5N 0.98N 4.9N 0.49N Problem 1994

Problem:

06 A long horizontal rod has a bead which can slide along its length and is initially placed at a distance L from one end A of the rod. The rod is set in angular motion about A with a constant angular acceleration, α. If the coefficient of friction between the rod and bead is µ, and gravity is neglected, then the time after which the bead starts slipping is : √µ/α µ/√α 1/ √ µα infinitesimal Problem 2000

Problem:

07 A small block is shot into each of the four tracks as shown below. Each of the tracks rises to the same height. The speed with which the block enters the tracks is the same in all cases. At the highest point of the track, the normal reaction is maximum in : Problem 2001

Problem:

08 An insect crawls up a hemispherical surface very slowly (see the figure). The coefficient of friction between the surface and the insect is 1/3. if the joining the center of the hemispherical surface to the insect makes an angle α with the vertical, the maximum possible value of α is given: cot α =3 tan α =3 sec α =3 cosec α =3 Problem 2001

Problem:

09 A string of negligible mass going over a clamped pulley of mass m supports a block of mass M as shown in the figure. The force on the pulley by the clamp is given by: √2Mg √2mg Asdf asdf Problem 2001

Problem:

10 The pulleys and strings shown in the figure are smooth and of negligible mass. For the system to remain in equilibrium, the angle θ should be : 0 0 30 0 45 0 60 0 Problem 2001

Problem:

11 What is the maximum value of the force F such that the block shown in the arrangement, does not move? 20N 10N 12N 15N Problem 2003

Problem:

12 A block P of mass m is placed on a horizontal frictionless plane. A second block of same mass m is placed on it and is connected to a spring of spring constant k, the two blocks are pulled by distance A. block Q oscillates without slipping. What is the maximum value of frictional force between the two blocks? kA/2 kA µ s mg zero Problem 2004

Problem:

13 A block of mass m is at rest under the action of force F against a wall as shown in figure. Which of the following statement is incorrect? f=mg [where f is the frictional force] F=N [where N is the normal force] F will not produce torque N will not produce torque Problem 2004

Problem:

14 System shown in figure is in equilibrium and at rest. The spring and string are massless, now the string is cut. The acceleration of mass 2m and m just after the string is cut will be : g/2 upwards, g downwards g upwards, g/2 downwards g upwards, 2g downwards 2g upwards, g downwards Problem 2006

SECTION – II:

SECTION – II OBJECTIVE QUESTIONS More than one options are correct

Problem:

01 A simple pendulum of length L and mass (bob) M is oscillating in a plane about a vertical line between angular limits -Φ and + Φ. For an angular displacement θ(|θ|<Φ), the tension in the string and the velocity of the bob are T and V respectively. The following relations hold good under the above conditions: T cos θ=Mg T-Mg cos θ= MV 2 /L The magnitude of the tangential acceleration of the bob =g sin θ T= Mg cos θ Problem 1981

Problem:

02 Problem 1986 A reference frame attached to the earth : Is an inertial by definition Cannot be an inertial frame because the earth is revolving round the sun Is an inertial frame because Newton's laws are applicable in this frame Cannot be an inertial frame because the earth is rotating about its own axis

SECTION – III:

SECTION – III SUBJECTIVE QUESTIONS

Problem:

01 Masses M 1 ,M 2 and M 3 are connected by strings of negligible mass which pass over massless and frictionless pulleys P 1 and P 2 as shown in fig. The masses move such that the portion of the string between P 1 and P 2 is parallel to the inclined plane and the portion of the string between P 2 and M 3 is horizontal. The masses M 2 and M 3 are 4.0 kg each and the coefficient of kinetic friction between the masses and the surfaces is 0.25. the inclined plane makes an angle of 37 0 with the horizontal. Problem 1981 If the mass M 1 moves downwards with a uniform velocity, find: The mass of M 1 The tension in the horizontal portion of the string. (g=9.8 m/s 2 , sin 37 0 3/5)

Problem:

02 A block of mass m rests on a horizontal floor with which it has a coefficient of static friction μ. It is desired to make the body move by applying the minimum possible force F. find the magnitude of F and the direction in which it has to be applied. Problem 1986

Problem:

03 Two blocks of mass 2.9 kg are suspended from a rigid support S by two inextensible wires each of length 1m (see fig.) the upper wire has a uniform mass of 0.2 kg/m. the whole system of blocks, wires and support have an upward acceleration of 0.2 m/s 2 . the acceleration due to gravity is 9.8 m/s 2 . ( i ) Find the tension at the midpoint of the lower wire. (ii)Find the tension at the midpoint of the upper wire. Problem 1989

Problem:

04 A hemispherical bowl of radius R=0.1 m is rotating about its own axis (which is vertical) with an angular velocity ω. A particle of mass 10 -2 kg on the frictionless inner surface of the bowl is also rotating with the same ω. The particle is at a height h from the bottom of the bowl. Obtain the relation between h and ω. What is the minimum value of ω needed, in order to have a non-zero value of h? It is desired to measure g (acceleration due to gravity) using the set-up by measuring h accurately. Assuming that R and ω are known precisely and that the least count in the measurement of h is 10 -4 m, what is minimum possible error ∆ g in the measured value of g ? Problem 1993

Problem:

05 A smooth semicircular wire track of radius R is fixed in a vertical plane (fig). One end of a massless spring of natural length 3R/4 is attached to the lowest point O of the wire track. A small ring of mass m which can slide on the track is attached to the other end of the spring. The ring is held stationary at point P such that the spring makes an angle 60 0 with the vertical. The spring constant K=mg/R. consider the instant when the ring is making an angle 60 0 with the vertical. The spring released Draw the free body diagram of the ring Determine the tangential acceleration of the ring and the normal reaction. Problem 1996

Problem:

06 Two blocks of mass M 1 = 10 kg and m 2 = 5 kg connected to each other by a massless inextensible string of length 0.3 m are placed along a diameter of turn table. The coefficient of friction between the table and m 1 is 0.5 while there is no friction between m 2 and the table. Is rotating with an angular velocity of 10 rad /s about a vertical axis passing through its center O. The masses are placed along the diameter of table on either side of the center O such that the mass m 1 is at a distance of 0.124 m from O. the masses are observed to be at rest with respect to an observer on the turn table. Calculate the frictional turn table. What should be the minimum angular speed of the turn table, so that the masses will slip from this position ? How should the masses be placed with the string remaining taut so that there is no frictional force acting on the mass m 1 ? Problem 1997

Problem:

07 Block a off mass m and block B of mass 2m are placed on a fixed trianglar wedge by means of a massless, in extensible string and a frictionless pulley as shown in figure. The wedge is inclined at 450 to the horizontal on both sides. The coefficient o friction between block A and the wedge is 2/3 and that between block B and the wedge is 1/3. If the system A and B is released from rest, find: ( i ) the acceleration of A, (ii) tension in the string and (iii) the magnitude and direction of the force of friction acting on a. Problem 1998

Problem:

08 In the figure masses m 1 , m 2 and M are 20 kg, 5 kg and 50 kg respectively. The coefficient of friction between M and ground is zero. The coefficient of friction between m 1 and M and that between m 2 and ground is 0.3 The pulleys and the strings are massless. The string is perfectly horizontal between P 1 and m 1 and also between P 2 and m 2 . The string is perfectly vertical between P 1 and P 2 . An external horizontal force F is applied to the mass M. Take g = 10 m/s 2 . Draw a free body diagram of mass M, clearly showing all the forces. Let the magnitude of the force of friction between m 1 and M be f1 and the between m 2 and ground be f 2 .for a particular force F it is found that f 1 = 2f 2 . Write equations of motion of all the masses. Find F, tension in the string and accelerations of the masses. Problem 2000

Problem:

09 Two blocks A and B of equal masses are release from an inclined plane of inclination 450 at t = 0. Both the blocks are initially at rest. The coefficient of kinetic friction between the block A and the inclined plane is 0.2 while it is 0.3 for block B. Initially the block A is √2 m behind the block B. When and where their front faces will come in a line. (Take g =10 m/s 2 ) Problem 2004

Problem:

10 Two identical ladders are arranged as shown in the figure. Mass of each ladder is M and length L. The system is in equilibrium. Find direction and magnitude of frictional force acting at A or B. Problem 2005

Problem:

11 A circular disc with a groove along its diameter is placed horizontally. A block of mass 1 kg is placed as shown. The coefficient of friction between the block and all surfaces of groove in contact is μ=2/5. The disc has an acceleration of 25 m/s 2 . Find the acceleration of the block with respect of disc. Problem 2006