# Engineering Physics Questions and Answers – Weight of a Body

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Weight of a Body”.

1. Assuming the earth to be a sphere of uniform mass density, how much would a body weigh half way down to the centre of the earth if it weighed 250N on the surface?
a) 125N
b) 250N
c) 0N
d) 125N

Explanation: Here mg = 250N, d = R/2
Acceleration due to gravity at depth d = R/2, below the earth’s surface will bw
gd=g(1-d/R)=g(1-(R/2)/R)=g/2
Therefore, new weight = mgd=mg/2=250/2=125N.

2. Calculate the force of attraction between two balls each of mass 1kg when their centres are 10cm apart. The value of gravitational constant G = 6.67×10-11 Nm2 kg(-2).
a) 6.67×10-11N
b) 6.67×10-10N
c) 6.67N
d) 6.67×1010 N

Explanation: Force of attraction,
F=G (m1 m2)/r2 = ((6.67×10-11)×1×1)/0.10=6.67×10-10 N.

3. If the kinetic energy of the satellite revolving in an orbit close to the earth’s surface happens to be doubled, what happens to the satellite?
a) It revolves faster
b) It revolves slower
c) It remains unaltered
d) It escapes

Explanation: When the kinetic energy of the satellite is doubled, its orbital velocity increases √2 times and becomes equal to the escape velocity. So the satellite will escape.

4. The escape velocity in earth is 11.2km/s. What will be its value on a planet whose radius is double the radius of the earth and eight times the mass of the earth?
a) 22.2km/s
b) 22.4km/s
c) 12km/s
d) 24.2km/s

Explanation:
vp/ve =√((2GMp)/Rp)×√(Rg/(2GMe )) = √(Mp/Me ×Re/Rp)
vp/ve = √(8×1/2)=2
vp=2ve=2×11.2=22.4km/s.

5. A spring balance is suspended from inside an artificial satellite revolving around the earth. If a body of mass 1kg is suspended from it, what would be its reading?
a) 1
b) 2
c) Depends on the mass of the satellite
d) 0

Explanation: If a body of mass 1 kg is suspended from a spring balance inside an artificial satellite revolving around the earth, its reading will be zero. This is because the satellite is in a state of free fall.
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6. Statement 1 – The earth is slowing down and as a result, the moon is coming nearer to it.
Statement 2 – The angular momentum of the system is not conserved.
a) Statement 1 and statement 2 are correct and statement 2 is the correct explanation of statement 1
b) Statement 1 and statement 2 are correct but statement 2 is not the correct explanation of statement 1
c) Statement 1 is true but statement 2 is false
d) Both statement 1 and 2 are false

Explanation: Both the statements are false. The earth is not slowing down. The speed of rotation of the earth about its axis remains constant. Further, the angular momentum of the earth-moon system is conserved.

7. Statement 1 – If a pendulum falls freely, then its time period is infinite.
Statement 2 – Free falling body has acceleration equal to g.
a) Statement 1 and statement 2 are correct and statement 2 is the correct explanation of statement 1
b) Statement 1 and statement 2 are correct but statement 2 is not the correct explanation of statement 1
c) Statement 1 is true but statement 2 is false
d) Both statement 1 and 2 are false

Explanation: Both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

8. Imagine a new planet having the same density as that of earth but it is 3 times bigger than the earth in its size. If the acceleration due to gravity on the surface of the earth is g and that on the surface of the new planet g is?
a) g=g/9
b) g=27g
c) g=9g
d) g=3g

Explanation:
g=4/3 πGRp
g=4/3 πGRp ρ=4/3 πG×3R×ρ
g=3g.

9. A ball dropped from a spacecraft is revolving around the earth at a height of 120km. What will happen to the ball?
a) It will fall down to the earth gradually
b) It will go very far in the space
c) It will continue to move with the same speed along the original orbit of the spacecraft
d) It will move with the same speed, tangentially to the spacecraft

Explanation: As no external torque is being applied, by the law of conservation of angular momentum, the ball will continue to move with the same angular velocity along the original orbit of the spacecraft.

10. G is called gravitation constant.
a) True
b) False

Explanation: G is called gravitation constant because the value of G is same for any pair of bodies in the universe. It does not depend on the nature of the medium between the two bodies or on the nature of the bodies themselves.

11. What is the ration of the force of attraction between two bodies kept in the air and the same distance apart in the water?
a) 2:1
b) 1:2
c) 1:1
d) 2:4

Explanation: The ratio of the force of attraction between two bodies kept in the air and the same distance apart in water is 1:1 because the gravitational force does not depend on the nature of the medium.

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