physics : class11 Angular Momentum : Second Law of Kepler : Gravitation MCQ Questions and Answers
Practice important
Angular Momentum
MCQ questions and answers.
Page 1
of
1
|
10
MCQ Questions
1. The angular momentum of a planet moving around the Sun remains constant because the gravitational force produces
A.
zero torque about the Sun
B.
constant linear speed
C.
constant acceleration in every direction
D.
zero gravitational force
Correct Answer:
zero torque about the Sun
Explanation:
The gravitational force acts along the line joining the planet and the Sun, so its torque about the Sun is zero. Therefore, the planet's angular momentum about the Sun is conserved.
2. For a planet of mass m moving with speed v at a distance r from the Sun, with velocity perpendicular to r, its angular momentum is
A.
mv/r
B.
mvr
C.
mr/v
D.
mv²r
Correct Answer:
mvr
Explanation:
When the velocity is perpendicular to the radius vector, angular momentum is L = mvr.
3. According to Kepler's second law, a planet sweeps out equal areas in equal intervals of time because its
A.
linear momentum is always zero
B.
angular momentum about the Sun is conserved
C.
distance from the Sun is always constant
D.
speed is always constant
Correct Answer:
angular momentum about the Sun is conserved
Explanation:
Conservation of angular momentum gives constant areal velocity, which means the planet sweeps out equal areas in equal times.
4. The angular momentum of a planet about the Sun is directed
A.
along the radius vector
B.
opposite to its velocity
C.
perpendicular to the plane of its orbit
D.
toward the center of the Sun
Correct Answer:
perpendicular to the plane of its orbit
Explanation:
Angular momentum is the vector product of the position vector and linear momentum, so it is perpendicular to the plane containing them, which is the orbital plane.
5. If the distance of a planet from the Sun decreases while its angular momentum remains constant, its orbital speed
A.
decreases
B.
increases
C.
becomes zero
D.
remains unchanged in all cases
Correct Answer:
increases
Explanation:
For nearly perpendicular motion, angular momentum is L = mvr. If L and m remain constant, a decrease in r requires an increase in v.
6. The areal velocity of a planet is related to its angular momentum L and mass m by
A.
dA/dt = L/m
B.
dA/dt = 2L/m
C.
dA/dt = L/(2m)
D.
dA/dt = m/(2L)
Correct Answer:
dA/dt = L/(2m)
Explanation:
The angular momentum of a planet is related to areal velocity by L = 2m(dA/dt). Hence, dA/dt = L/(2m).
7. At the closest point to the Sun, a planet has distance r and speed v. At the farthest point, its distance is R and its speed is V. For conserved angular momentum, which relation is correct?
A.
rv = RV
B.
rV = Rv
C.
r + v = R + V
D.
r/v = R/V
Correct Answer:
rv = RV
Explanation:
At the closest and farthest points, the velocity is perpendicular to the radius. Conservation of angular momentum gives mrv = mRV, so rv = RV.
8. If no external torque acts on a planet about the Sun, which quantity remains constant?
A.
Angular momentum
B.
Distance from the Sun
C.
Direction of velocity
D.
Area swept in every second for a changing time interval
Correct Answer:
Angular momentum
Explanation:
The rate of change of angular momentum equals the external torque. With zero external torque, angular momentum remains constant.
9. A planet moves faster when it is closer to the Sun mainly to conserve its
A.
mass
B.
angular momentum
C.
radius
D.
gravitational constant
Correct Answer:
angular momentum
Explanation:
As the planet's distance from the Sun decreases, its speed increases so that its angular momentum about the Sun remains conserved.
10. The SI unit of angular momentum is
A.
newton
B.
joule
C.
kilogram metre squared per second
D.
kilogram metre per second
Correct Answer:
kilogram metre squared per second
Explanation:
Angular momentum is L = r × p. Its SI unit is metre multiplied by kilogram metre per second, or kilogram metre squared per second.
Short Questions and Answers
Practice short questions and answers related to
Angular Momentum
.
Short questions are currently unavailable for this page.