Directions : Each of these questions contain two statements, Assertion and Reason. Each of these questions also has four alternative choices, only one of which is the correct answer. You have to select one of the codes (a), (b), (c) and (d) given below.
(a) Assertion is correct, reason is correct; reason is a correct explanation for assertion.
(b) Assertion is correct, reason is correct; reason is not a correct explanation for assertion
(c) Assertion is correct, reason is incorrect
(d) Assertion is incorrect, reason is correct.
Q.1. Assertion: A body loses weight when it is at the centre of the earth.
Reason: At the centre of earth, g = 0. Therefore, weight = mg = 0.
Q.2. Assertion : If earth suddenly stops rotating about its axis, then the value of acceleration due to gravity will become same at all the places.
Reason : The value of acceleration due to gravity depends upon the rotation of the earth.
Q.3. Assertion : A body becomes massless at the centre of earth.
Reason : This follows from g’ = g (1 – d/R)
AnswerAnswer: (d) At the centre of the earth, weight is zero but mass cannot be and never zero.
Q.4. Assertion : Space rockets are usually launched in the equatorial line from west to east.
Reason : The acceleration due to gravity is minimum at the equator.
Q.5. Assertion : Gravitational force between two particles is negligibly small compared to the electrical force.
Reason : The electrical force is experienced by charged particles only.
Q.6. Assertion: The gain in potential energy of an object of mass m raised to height equal to the radius of earth is mgR/2
Reason: Kinetic energy at surface = P.E at the top mv2/2 and at the top v = √gR . PE = mgR/2.
Q.7. Assertion: The value of acceleration due to gravity i.e. ‘g’ is different at different places on the surface of earth.
Reason: Earth is flattened at poles and bulging out at the equator. Therefore radius is smaller at poles and larger at equator and g α 1/R2, so, g is smaller at equator than at poles.
Q.8. Assertion : Smaller the orbit of the planet around the sun, shorter is the time it takes to complete one revolution.
Reason : According to Kepler’s third law of planetary motion, square of time period is proportional to cube of mean distance from sun.
Q.9. Assertion : Moon travellers tie heavy weight at their back before landing on the moon.
Reason : The acceleration due to gravity on moon is smaller than that of earth.
AnswerAnswer: (a) To counter balance the effect of gravity.
Q.10. Assertion : Generally, the path of a projectile from the earth is parabolic but it is elliptical for projectiles going to a very large height.
Reason : The path of a projectile is independent of the gravitational force of earth.
Q.11. Assertion : Gravitational potential is maximum at infinity.
Reason : Gravitational potential is the amount of work done to shift a unit mass from infinity to a given point in gravitational attraction force field.
Q.12. Assertion : The tidal waves in sea are primarily due to the gravitational effect of earth.
Reason : The intensity of gravitational field of earth is maximum at the surface of earth.
Q.13. Assertion : For the planets orbiting around the sun, angular speed, linear speed and K.E. changes with time, but angular momentum remains constant.
Reason : No torque is acting on the rotating planet. So its angular momentum is constant.
Q.14. Assertion : Gravitational potential of earth at every place on it is negative.
Reason : Every body on earth is bound by the attraction of earth.
AnswerAnswer: (a) Because gravitational force is always attractive in nature and every body is bound by this gravitational force of attraction of earth.
Q.15. Assertion: Planets appear to move slower when they are farther from the sun than when they are nearer.
Reason: All planets move in elliptical orbits with sun at one of the foci of the ellipse.