Skip to content

#Kepler's third law

20 public questions tagged with this topic.

A satellite near Earth has a period of 89 minutes. What is its period at h\=7RE? (RE\=6.4×106m)

T2∝(RE+h)3. T02 = kRE3, h = 7RE, r = 8RE. T2 = k(8RE)3 = 512kRE3. T = T0512 = 89×22.63≈2014min. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 2010 min. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: Halliday & Resnick, Fundamentals of Physics, 11th ed., Chapter 13: Gravitation.

A satellite near Earth has a period of 86 minutes. What is its period at h\=5RE? (RE\=6.4×106m)

T2∝(RE+h)3. T02 = kRE3, h = 5RE, r = 6RE. T2 = k(6RE)3 = 216kRE3. T = T0216 = 86×14.7≈1264min. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 1270 min. This satisfies dimensional consistency and physical conditions given, so option D is scientifically correct.

Ref: Halliday & Resnick, Fundamentals of Physics, 11th ed., Chapter 13: Gravitation.

Why does a satellite in a higher orbit have a longer orbital period?

T2∝r3 for satellites. A higher orbit (larger r) increases T2 by r3, so the period T increases as the radius grows, reflecting weaker gravitational pull at greater distances. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Gravitational force decreases. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: Halliday & Resnick, Fundamentals of Physics, 11th ed., Chapter 13: Gravitation.

Which of the following statements is correct about Kepler’s third law?

T2∝a3, meaning the period squared is proportional to the semi-major axis cubed, making option 2 correct. As per NCERT, applying relevant law/formula with correct units and sign convention leads to Period squared is proportional to distance cubed. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: NCERT Class 11 Physics, Thermal Properties and Gravitation.

A planet orbits the Sun with a period of 7 years. If Earth’s orbital radius is 1.5×1011m, what is its semi-major axis?

Kepler’s third law: Tp2TE2 = ap3aE3. TE = 1year, Tp = 7years, aE = 1.5×1011m. 7212 = ap3(1.5×1011)3. 49 = ap33.375×1033. ap3 = 49×3.375×1033 = 1.65375×1035. ap = (1.65375×1035)1/3≈5.49×1011m. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 5.5 × 10¹¹ m. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: Halliday & Resnick, Fundamentals of Physics, 11th ed., Chapter 13: Gravitation.

A moon orbits a planet with a period of 9 days and radius 6×108m. What is the planet’s mass? (G\=6.67×10−11N m2/kg2,1day

M = 4π2r3GT2. T = 9×86400 = 7.776×105s. T2 = 6.046×1011s2. r3 = (6×108)3 = 2.16×1026m3. M = 4×(3.14)2×2.16×10266.67×10−11×6.046×1011. M = 8.51×10264.033×101≈2.11×1025kg. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 2.1 × 10²⁵ kg. This satisfies dimensional consistency and physical conditions given, so option B is scientifically correct.

Ref: Halliday & Resnick, Fundamentals of Physics, 11th ed., Chapter 13: Gravitation.

A planet orbits the Sun with a period of 6 years. If Earth’s orbital radius is 1.5×1011m, what is its semi-major axis?

Kepler’s third law: Tp2TE2 = ap3aE3. TE = 1year, Tp = 6years, aE = 1.5×1011m. 6212 = ap3(1.5×1011)3. 36 = ap33.375×1033. ap3 = 36×3.375×1033 = 1.215×1035. ap = (1.215×1035)1/3≈4.95×1011m. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 5.0 × 10¹¹ m. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: Halliday & Resnick, Fundamentals of Physics, 11th ed., Chapter 13: Gravitation.

A satellite near Earth has a period of 90 minutes. What is its period at h\=3RE? (RE\=6.4×106m)

T2∝(RE+h)3. T02 = kRE3, h = 3RE, r = 4RE. T2 = k(4RE)3 = 64kRE3. T = T064 = 90×8 = 720min. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 720 min. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: Halliday & Resnick, Fundamentals of Physics, 11th ed., Chapter 13: Gravitation.

A satellite orbits a planet at 2.5×107m from its center with a period of 5 hours. What is the planet’s mass? (G\=6.67×10

M = 4π2r3GT2. T = 5×3600 = 18000s, T2 = 3.24×108s2. r3 = (2.5×107)3 = 1.5625×1022m3. M = 4×(3.14)2×1.5625×10226.67×10−11×3.24×108. M = 6.158×10232.161×10−2≈2.85×1025kg. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 2.9 × 10²⁵ kg. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: Halliday & Resnick, Fundamentals of Physics, 11th ed., Chapter 13: Gravitation.

A satellite orbits a planet at 2×106m from its center with a period of 2 hours. What is the planet’s mass? (G\=6.67×10−1

T2 = 4π2GMr3. M = 4π2r3GT2. T = 2×3600 = 7200s, T2 = 5.184×107s2. r3 = (2×106)3 = 8×1018m3. M = 4×(3.14)2×8×10186.67×10−11×5.184×107. M = 3.155×10203.458×10−3≈9.12×1022kg. As per NCERT, applying relevant law/formula with correct units and sign convention leads to 9.1 × 10²² kg. This satisfies dimensional consistency and physical conditions given, so option C is scientifically correct.

Ref: Halliday & Resnick, Fundamentals of Physics, 11th ed., Chapter 13: Gravitation.