# Engineering Physics Questions and Answers – Orbital Velocity

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Orbital Velocity”.

1. The mass of the moon is 1% of the mass of the earth. The ratio of gravitational pull on moon and that of moon in earth will be ___________
a) 1:1
b) 1:10
c) 1:100
d) 2:1

Explanation: Gravitational forces are mutually equal and opposite.

2. If the earth loses its gravity, then for a body ___________
a) Weight becomes zero
b) Mass becomes zero
c) Neither mass nor weight is zero
d) Both mass and weight are zero

Explanation: Weight = mg
As g becomes zero, weight is zero. Mass is the quantity of matter which is independent of g.

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

Explanation: In the absence of external torque the ball will continue to move with the same speed along the original orbit of spacecraft.

4. The velocity with which a projectile must be fired so that it escapes the earth’s gravitational field doesn’t depend on ___________
a) Mass of the earth
b) Mass of the projectile
d) Universal gravitational constant

Explanation: Escape velocity does not depend on the mass of the projectile.

5. The escape velocity of a projectile from the earth is approximately ___________
a) 7km/sec
b) 11.2km.sec
c) 112km/sec
d) 1.1km/sec

Explanation: From the earth’s surface,
ve=√2gR=11.2km/sec.

6. The escape velocity of a body projected vertically upwards from the surface of the earth is 11km/sec. If the body is projected at an angle of 45° with the vertically, the escape velocity will be ___________
a) 22km/sec
b) 11km/sec
c) 11√2km/sec
d) 11/√2km/sec

Explanation: Escape velocity does not depend on the angle of the projection of the projectile. Hence the escape velocity remains the same as the earlier condition.

7. The escape velocity from the earth is 11.2km/sec. Another plant is having a mass 1000 times and radius 10 times that of the earth, then escape velocity at that planet will be ___________
a) 11.2km/sec
b) 112km/sec
c) 1.12km/sec
d) 1120km/sec

Explanation: ve=√(2GM/R)=11.2km/sec
(ve)=√((2G×100M)/(R/4))=2/9 √(2GM/R)
(ve)=2/9×11.2=2.5km/sec.

8. What is Black hole?
a) Super surface of the atmosphere
b) Ozone layer
c) Super dense planetary material
d) A hole on the surface of the earth

Explanation: Black hole is a super dense planetary material formed due to the continued compression the core of a star during a supernova explosion.

9. If the orbital radius of the earth is made 4 times, then find the duration of the year if earlier it was T?
a) T
b) 2T
c) 4T
d) 8T

Explanation: T2/T1 =(4r/r)(3/2)=(4)(3/2)=8
T2=8T1=8T.

10. If radius of the earth is reduced, then ___________
a) Time duration is reduced
b) Earth rotates slower
c) Time period of earth decreases
d) Duration of day increases

Explanation: I=2/5 MR2
When R decreases, the moment of inertia decreases.
But Iω=consatnt
ω=2π/T increases
Hence the period of rotation T decreases.

11. A point mass m is placed inside a spherical shell of radius R and mass M at a distance R/2 from the centre of the shell. The gravitational force exerted by the shell on the point mass is ___________
a) GMm/R2
b) GMm/R
c) Zero
d) 4GMm/R2

Explanation: At the inner position of the shell, the gravitational field intensity (E) is zero.
Therefore, F=mE=0.

12. A man is standing on an international space station which is orbiting earth at an altitude 520km with a constant speed 7.6km/s. If the man’s weight is 50kg, his acceleration is ___________
a) 7.6 km/s2
b) 7.6 m/s2
c) 8.4 m/s2
d) 10 m/s2

Explanation: gh=R2/(R+h)2 g
gh=(6400×103)2/[(6400+520)×103]2 ×10=8.4m/s2.

Sanfoundry Global Education & Learning Series – Engineering Physics.

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