University:
Cypress College
Course:
PHYS 201 C | College Physics I
Academic year:

2021
Views:

8

Pages:

42
Author:

NikkiP24

Chapter 4: Laws of Motion EXERCISES PAGES 73-77 Exercises Q1. (i) | Page 73 Choose the correct answer. Consider the following pair of forces of equal magnitude and opposite directions: P. Gravitational forces exerted on each other by two-point masses separated by a distance. Q. Couple of forces used to rotate a water tap. R. Gravitational force and normal force experienced by an object kept on a table. For which of these pair/pairs the two forces do not cancel each other's translational effect? 1. Only P 2. Only P and Q 3. Only R 4. Only Q and R SOLUTION Only Pie, Gravitational forces exerted on each other by two-point masses separated by a distance. Exercises Q 1. (ii)| Page 73 Choose the correct answer. Consider following forces: (w) Force due to tension along a string, (x) Normal force given by a surface, (y) Force due to air resistance, and (z) Buoyantforce or upthrust given by a fluid Which of these are electromagnetic forces? 1. Only w, y and z 2. Only w. x andy 3. Only x, y and z 4. All four SOLUTION All four. Exercises Q1. (iii) | Page 74 Choose the correct answer. At a given instant three-point masses m, 2m and 3m are equidistant from each other. Consider only the gravitational forces between them. Select correct statements for this instance only: 1. Mass m experiences maximum force. 2. Mass 2m experiences maximum force. 3. Mass 3m experiences maximum force. 4. All masses experience force of same magnitude. SOLUTION Mass 3m experiences maximum force. Exercises Q 1. (iv) | Page 74 Choose the correct answer. The rough surface of a horizontal table offers a definite maximum opposing force to initiate the motion of a block along with the table, which is proportional to the resultant normal force given by the table. Forces F1 and F2 act at the same angle T with the horizontal and both are just initiating the sliding motion of the block along with the table. Force Fi is a pulling force while the force F2 is a pushing force. F2 > F1, because 1. Component of F₂ adds up to weight to increase the normal reaction 2. Component of F₁ adds up to weight to increase the normal reaction. 3. Component of F2 adds up to the opposing force. 4. Component of Fi adds up to the opposing force. SOLUTION Component of F₂ adds up to weight to increase the normal reaction Exercises Q 1. (v) | Page 74 Choose the correct option. A mass 2m moving with some speed is directly approaching another mass m moving with double speed. After some time, they collide with a coefficient of restitution 0.5. The ratio of their respective speeds after the collision is 1. 2/3 2 3/2 3.2 4. 1/2 SOLUTION 3/2 Exercises Q1. (vi) | Page 74 Choose the correct answer. A uniform rod of mass 2m is held horizontal by two sturdy, practically inextensible vertical strings tied at its ends. A boy of mass 3m hangs himself at one-third length of the rod. The ratio of the tension in the string close to the boy to that in the other string is 1.2 2 1.5 3. 4/3 4, 5/3 SOLUTION 1.5 Exercises Q1. (vii) | Page 74 Choose the correct answer. Select the wrong statement about the centre of mass: 1. Centre of the mass of a 'C' shaped uniform rod can never be a pointon that rod. 2. If the line of action of a force passes through the center of mass, the moment of that force is zero. 3. Centre of a mass of our Earth is not at its geometrical centre. 4. While balancing an object on a pivot, the line of action of the gravitational force of the earth passes through the center of mass of the object. SOLUTION While balancing an object on a pivot, the line of action of the gravitational force of the earth passes through the center of mass of the object. Exercises Q 1. (viii) | Page 74 Choose the correct answer. For which of the following objects will the center of mass not be at their geometrical center? (1) An egg (II) a cylindrical box full of rice (III) a cubical box containing assorted sweets 1. Only (1) 2. Only (1) and (II) 3. Only (III) 4. All (I), (II) and (III) SOLUTION All (1), (II) and (III) Exercises Q 2. (1) | Page 74 Answer the following question. In the following table, every entry on the left column can match with any number of entries on the right side. Pick up all those and write respectively against (1), (ii), (iii) and (iv) Name of the force Type of the force A Force due to tension in a string P EM force B Normal force Q Reaction force C Frictional force R Conservative force D Resistive force offered by air or water for objects moving through it. S Nonconservative force SOLUTION A. Force due to tension in a string: Electromagnetic (EM) force, reaction force, non-conservative force. B. Normal force: Electromagnetic (EM) force, non-conservative force, Reaction force C. Frictional force: Electromagnetic (EM) force, reaction force, non-conservative force. D. Resistive force offered by air or water for objects moving through it: Electromagnetic (EM) force, non-conservative force.