Physics : Gravitation : Book Back Choose the correct Answers with Solution, One Mark and Multiple choice questions with Answers and Solution

__Gravitation (Physics)__

__Multiple Choice Questions__

**1.**** The linear momentum and position vector of the planet is perpendicular to each other at**

(a) perihelion and aphelion

(b) at all points

(c) only at perihelion

(d) no point

**Answer : a) perihelion and aphelion **

**Solution :**

L = mv × r

Here, *L, r* and *v* are mutually perpendicular. So. A
and P ate 90° in two position because it is elliptical orbit.

**2.**** If the masses of the Earth and Sun suddenly double, the gravitational force between them will**

(a) remain the same

(b) increase 2 times

(c) increase 4 times

(d) decrease 2 times

**Answer : c) increase 4 times **

**Solution :**

If mass of earth and sun is doubled then the force?

F_{1} = GM_{E}M_{S} / R^{2}

F_{2} = [ G(2M_{E})(2M_{S}) ] / [ R^{2
}] = 4GM_{E}M_{S} / R^{2 }

F_{2} = 4F_{1}

**Answer : a) r _{2} / r_{1}**

**Solution :**

L_{1} = mv_{1} , r_{1} & L_{2}
= mv_{2} r_{2}

L_{1 }= L_{2}

mv_{1} r_{1} = mv_{2} r_{2}

V_{1} / V_{2} = r_{2} / r_{1} (∴ v ∝ 1 / r)

**3.**** A planet moving along an elliptical orbit is closest to the Sun at distance r1 and farthest away at a distance of r2. If v1 and v2 are linear speeds at these points respectively. Then the ratio V1/V2 is**

**Answer : a) r _{2} / r_{1}**

**Solution :**

L_{1} = mv_{1} , r_{1} & L_{2}
= mv_{2} r_{2}

L_{1 }= L_{2}

mv_{1} r_{1} = mv_{2} r_{2}

V_{1} / V_{2} = r_{2} / r_{1} (∴ v ∝ 1 / r)

**4. The time period of a satellite orbiting Earth in a cirular orbit is independent of .**

(a) Radius of the orbit

(b) The mass of the satellite

(c) Both the mass and radius of the orbit

(d) Neither the mass nor the radius of its orbit

**Answer : b) The mass of the satellite **

**Solution :**

T = 2π √[Rɛ / g]

Independent of mass of the satellite.

**5. If the distance between the Earth and Sun were to be doubled from its present value, the number of days in a year would be**

(a) 64.5

(b) 1032

(c) 182.5

(d) 730

**Answer : b) 1032**

**Solution :**

b) T^{2} ∝ a^{3}

T_{1}^{2 }= const. a_{1}^{3} ⇒ T_{1}^{2 }/ a_{1}^{3 }= const

T_{2}^{2 }= const. a_{2}^{3} ⇒ T_{2}^{2 }/ a_{2}^{3 }= const

(1) = (2)

T_{1}^{2 }/ a_{1}^{3} = T_{2}^{2
}/ a_{2}^{3}

a_{1} = a

a_{2} = 2a

T_{2}^{2} = T_{1}^{2 }(2a / a )^{3}

T_{2}^{2} = 2 × 2 × 2 × T_{1}^{2}

T_{2} = √[4 × 2] × 365

T_{2} = 2 × √2 × 365

T_{2} = 1032.22 days

**6. According to Kepler’s second law, the radial vector to a planet from the Sun sweeps out equal areas in equal intervals of time. This law is a consequence of**

(a) conservation of linear momentum

(b) conservation of angular momentum

(c) conservation of energy

(d) conservation of kinetic energy

**Answer : b) Conservation of
angular momentum**

**7. The gravitational potential energy of the Moon with respect to Earth is**

(a) always positive

(b) always negative

(c) can be positive or negative

(d) always zero

**Answer : b) always negative**

**8. The kinetic energies of a planet in an elliptical orbit about the Sun, at positions A, B and C are KA, KB and KC respectively. AC is the major axis and SB is perpendicular to AC at the position of the Sun S as shown in the figure. Then**

(a) KA > KB >KC

(b) KB < KA <KC

(c) KA < KB <KC

(d) KB > KA >KC

**Answer: a) K _{A}>K_{B}>K_{C}**

**Solution :**

KE = Gm_{E}m_{S} / (R_{E} + h)

KE ∝ 1 / R_{e}↓

K_{A} > K_{B} > K_{C}

**9. The work done by the Sun’s gravitational force on the Earth is**

(a) always zero

(b) always positive

(c) can be positive or negative

(d) always negative

**Answer : c) can be positive
or negative**

**10.**** If the mass and radius of the Earth are both doubled, then the acceleration due to gravity g'**

(a) remains same

(b) g/2

(c) 2g

(d) 4g

**Answer: b) g / 2**

**Solution: **

g = GM / R^{2}

g = G(2M) / (2R)^{2} = 2GM / 4R^{2} = 1/2 (GM /
R^{2})

g = g / 2

**11. The magnitude of the Sun’s gravitational field as experienced by Earth is**

(a) same over the year

(b) decreases in the month of January and increases in the month of July

(c) decreases in the month of July and increases in the month of January

(d) increases during day time and decreases during night time.

**Answer : c) decreases in the month of July and increases in the
month of January**

**12. If a person moves from Chennai to Trichy, his weight**

(a) increases

(b) decreases

(c) remains same

(d) increases and then decreases

**Ans : b) decreases**

Solution:

Chennai 13^{o}

Trichy 11^{o}

g ∝ 1 / R

**13. An object of mass 10 kg is hanging on a spring scale which is attached to the roof of a lift. If the lift is in free fall, the reading in the spring scale is**

(a) 98 N

(b) zero

(c) 49 N

(d) 9.8 N

**Answer: b) Zero**

**14. If the acceleration due to gravity becomes 4 times its original value, then escape speed**

(a) remains same

(b) 2 times of original value

(c) becomes halved

(d) 4 times of original value

**Answer : b) 2 times of original value **

**Solution :**

V_{e} = √[2gR]

g = 9.8ms^{-2} .

V´_{e} = √[2(4g)R]

V´_{e} = 2√(2gR) = 2V_{e}

**15. The kinetic energy of the satellite orbiting around the Earth is**

(a) equal to potential energy

(b) less than potential energy

(c) greater than kinetic energy

(e) zero

**Answer : b) Less than potential energy **

**Solution :**

KE = 1/2 [ Gm_{E}m_{S} / (R_{e} + h) ]

U = − Gm_{E}m_{S} / (R_{E} + h)

∴ KE = U / 2

KE < U

1) a 2) c 3) a 4) b 5) b

6) b 7) b 8) a 9) c 10) b

11) c 12) a 13) b 14) b 15) b

Tags : Gravitation | Physics , 11th Physics : UNIT 6 : Gravitation

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11th Physics : UNIT 6 : Gravitation : Choose the correct answers | Gravitation | Physics

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