Astrophysics — Free IB MYP5 Physics Questions

1QuestionRole of gravity in maintaining orbitsConcept Practice

2 marks~3 minCriterion D

A communication satellite orbits Earth at an altitude of approximately 35 800 km in a geostationary orbit.

a

Explain how gravity keeps the satellite moving in a circular orbit rather than travelling in a straight line. [1]

b

A government agency is deciding whether to fund a new geostationary satellite network. Identify one societal impact — positive or negative — that could result from this technology, and explain why this impact is significant. [1]

Solutions

2QuestionConcept Practice

2 marks~3 minCriterion A

The diagram shows Saturn (centre C) with ring particle P orbiting at 120,000 km from C. A dashed arrow at P indicates its instantaneous velocity, tangent to the orbit.

(a) State the name of the force that keeps P in its circular orbit and identify the direction of this force relative to the line CP. [2]

Solutions

3QuestionEvidence supporting Big BangConcept Practice

2 marks~3 minCriterion A

A simplified absorption spectrum from a distant galaxy shows a hydrogen absorption line at a rest wavelength of

656.3 \, \text{nm}

, as measured in a laboratory on Earth. The same absorption line observed in the galaxy's spectrum appears at

\mathbf{699.2 \, \text{nm}}

.

a

Deduce the direction of the shift of the observed absorption line relative to the rest wavelength. [1]

b

Explain what this shift indicates about the motion of the galaxy relative to Earth. [1]

Solutions

4QuestionSteady State Theory (contrast with Big Bang)Concept Practice

2 marks~3 minCriterion D

A museum curator is designing an exhibit contrasting the Big Bang Theory and the Steady State Theory. The Steady State Theory proposed an eternal, unchanging universe, while the Big Bang Theory describes a universe with a definite beginning approximately 13.8 billion years ago.

a

Describe one way the shift from the Steady State Theory to the Big Bang Theory changed public understanding of the universe's origin. [1]

b

Explain the significance of this theoretical shift for science education. [1]

Solutions

5QuestionAssessment Practice

5 marks~8 minCriterion D

A space agency uses a spectrometer aboard an orbiting telescope to study an exoplanet's atmosphere during a transit. As starlight filters through the atmosphere, certain wavelengths are absorbed, producing a characteristic spectrum. Scientists compare this spectrum with laboratory reference spectra of gases including

O_2

,

CH_4

,

H_2O

, and

CO_2

.

a

Explain how absorption spectra allow scientists to identify specific gases in an exoplanet's atmosphere. In your answer, refer to quantized energy levels and characteristic wavelengths. [2]

b

Discuss the advantages and limitations of using transit spectroscopy to assess whether an exoplanet could support life, considering signal-to-noise ratio, Earth's atmospheric interference, and the interpretation of biosignature gases. [3]

Solutions

6QuestionDefinition of a planetAssessment Practice

5 marks~8 minCriterion C

The table below shows data for three solar system objects.

Object	Mass (Earth masses)	Orbital clearing status
Ceres	$0.00016$	Not cleared
Pluto	$0.0022$	Not cleared
Eris	$0.0028$	Not cleared

a

State the three criteria in the IAU definition of a planet. [1]

b

Using the data, explain the relationship between mass and the ability to clear an orbital neighbourhood. [2]

c

A scientist argues that if Eris were given enough additional mass, it would eventually be reclassified as a planet. Evaluate this claim, identifying what other conditions would also need to be satisfied. [2]

Solutions

7QuestionDefinition of a planetAssessment Practice

5 marks~8 minCriterion C

The International Astronomical Union (IAU) defines a planet as a celestial body that: (a) orbits the Sun; (b) has sufficient mass for self-gravity to pull it into a nearly round (hydrostatic equilibrium) shape; (c) has cleared the neighbourhood around its orbit. A body satisfying only (a) and (b) is classified as a dwarf planet.

Data for three Solar System bodies:

Orbital radius (AU): Ceres 2.77, Pluto 39.5, Eris 67.7

Mass (kg): Ceres

9.4 \times 10^{20}

, Pluto

1.3 \times 10^{22}

, Eris

1.6 \times 10^{22}

Shape: all three spherical

Neighbourhood status: Ceres — not cleared (shares orbit with asteroid belt); Pluto — not cleared (shares orbit with Kuiper Belt objects); Eris — not cleared (shares orbit with trans-Neptunian objects)

(a) State which IAU criterion none of the three bodies satisfies, and identify the evidence from the data that supports this. [1]

(b) Explain why all three bodies satisfy IAU criteria (a) and (b), using specific data from the table. [2]

(c) Evaluate whether Ceres, Pluto, and Eris should be classified as planets or dwarf planets according to the IAU definition. Justify your conclusion by applying all three criteria to each body. [2]

Solutions

8QuestionFormation of the solar system (nebular hypothesis – basic idea)Assessment Practice

8 marks~12 minCriterion A

The nebular hypothesis proposes that the Sun and planets formed from a rotating cloud of gas and dust. The protosolar cloud had a moment of inertia of

9.0 \times 10^{46}\ \text{kg m}^2

and rotated once every

10^6

years. After collapse, the Sun has a moment of inertia of

3.0 \times 10^{41}\ \text{kg m}^2

and an actual rotation period of 25 days.

a

Calculate the angular velocity of the protosolar cloud. [2]

b

Using conservation of angular momentum, deduce the expected rotation period of the Sun after collapse. Compare your result with the actual period and suggest one reason for any discrepancy. [2]

c

Calculate the change in rotational kinetic energy between the cloud and the Sun. Justify, with reference to your calculated values, angular momentum conservation, and energy transformation, why the nebula flattened into a disk rather than collapsing into a sphere. [4]

Solutions

9QuestionHuman impact on space (space debris)Assessment Practice

7 marks~11 minCriterion B

Three space debris objects, each with mass 10 kg, orbit Earth in a circular low Earth orbit at 400 km altitude. Their orbital decay times differ due to their shapes and cross-sectional areas. Atmospheric drag is described by:

F_d = \frac{1}{2} \rho v^2 C_d A

where

\rho

is atmospheric density,

v

is orbital speed,

C_d \approx 2.2

for all objects, and

A

is cross-sectional area perpendicular to motion.

Object shape	Cross-sectional area $A$ (m²)	Decay time $T$ (days)
Sphere	0.5	120
Cube	0.8	75
Thin sheet	2.0	30

a

Deduce the mathematical relationship between cross-sectional area and decay time using the data provided. [2]

b

A fourth object of identical mass and altitude has a cross-sectional area of 1.2 m². Show that its decay time is 50 days. [2]

c

Explain how cross-sectional area determines the rate of orbital decay, referring to the drag force equation and the effect of drag on orbital energy and altitude over time. [3]

Solutions

10QuestionRelationship between distance and orbital periodAssessment Practice

8 marks~12 minCriterion B

The table below shows the mean orbital radius and orbital period for the first six planets of the Solar System.

Planet	Orbital radius $r$ (AU)	Orbital period $T$ (years)
Mercury	0.387	0.241
Venus	0.723	0.615
Earth	1.000	1.000
Mars	1.524	1.881
Jupiter	5.203	11.862
Saturn	9.537	29.457

a

Construct a table showing

r^3

and

T^2

for each planet, calculated to four significant figures. [2]

b

Plot

T^2

against

r^3

and interpret the graph to deduce the mathematical relationship between

T^2

and

r^3

. [3]

c

Uranus has an orbital radius of 19.19 AU. Evaluate whether Kepler's Third Law can reliably predict the orbital period of Uranus, and calculate that period. [3]

Solutions

11QuestionFormation of stars and galaxiesAssessment Practice

7 marks~11 minCriterion B

The star formation rate (SFR) and average gas density

n

for five molecular clouds are given below.

Cloud	A	B	C	D	E
$n$ (atoms cm $^{-3}$ )	100	200	300	400	500
SFR (solar masses yr $^{-1}$ )	0.5	2.0	4.5	8.0	12.5

The Schmidt–Kennicutt law states that

\text{SFR} \propto n^{k}

.

a

Construct a log–log graph of SFR against

n

using the data above, and deduce the value of

k

. [4]

b

Using your value of

k

, predict the SFR for a cloud with

n = 600

atoms cm

^{-3}

. [1]

c

Evaluate whether the Schmidt–Kennicutt law is likely to remain valid for molecular clouds with

n < 10

atoms cm

^{-3}

. [2]

Solutions

12QuestionDefinition of CMBAssessment Practice

6 marks~9 minCriterion C

The Planck satellite maps the Cosmic Microwave Background (CMB) across multiple frequencies. Its detectors must distinguish the primordial CMB signal from foreground emissions: interstellar dust radiates in the infrared-to-microwave range, while synchrotron radiation is produced by high-energy electrons spiralling in the galaxy's magnetic field. Scientists apply multi-frequency algorithms to subtract these foregrounds, but residual uncertainties remain in the final CMB maps.

a

Define the Cosmic Microwave Background (CMB). [1]

b

Explain how interstellar dust and synchrotron radiation each interfere with the Planck satellite's detection of the CMB signal. [2]

c

Evaluate whether foreground contamination invalidates the Big Bang model or affects only the precision of cosmological measurements. [3]

Solutions

13QuestionEvidence supporting Big BangAssessment Practice

5 marks~8 minCriterion C

Five distant galaxies were observed as part of a study into the expanding universe. The Hubble constant

H_0

relates recessional velocity

v

to distance

d

by

v = H_0 d

.

Distance (Mpc)	100	200	300	400	500
Recessional velocity (km/s)	2200	4400	6600	?	11000

a

Construct a graph of recessional velocity (y-axis) against distance (x-axis) for galaxies at 100, 200, 300, and 500 Mpc. Draw a best-fit straight line through the data. [1]

b

Deduce the value of

H_0

from the gradient of your line, including appropriate units. [2]

c

A student claims that galaxy D, at 400 Mpc, does not fit the pattern shown by the other four galaxies. Using your value of

H_0

, calculate the expected recessional velocity of galaxy D and evaluate whether the student's claim is supported. [2]

Solutions

14QuestionUniverse beginning from a singularityAssessment Practice

4 marks~6 minCriterion B

Astronomers measure the recession velocities of six galaxies at known distances from Earth.

Galaxy	A	B	C	D	E	F
Distance (Mpc)	10	20	30	40	50	60
Recession velocity (km/s)	700	1400	2100	2800	3500	4200

a

Construct a graph of recession velocity (y-axis) against distance (x-axis) and describe the pattern shown. [1]

b

Deduce the relationship between recession velocity

v

and distance

d

, expressing it as an equation with a numerical constant. [2]

c

A seventh galaxy has a recession velocity of 5600 km/s. Evaluate whether this galaxy's distance is consistent with the relationship you found in (b), and state one assumption you must make. [1]

Solutions

15QuestionSteady State Theory (contrast with Big Bang)Assessment Practice

6 marks~9 minCriterion A

The COBE/FIRAS satellite measured the cosmic microwave background (CMB) temperature as 2.725 K. Two cosmological models make different predictions:

- Steady State model: predicts no CMB, so predicted temperature = 0 K
- Big Bang model: predicts CMB temperature = 2.7 K

Use the formula throughout:

\text{percentage discrepancy} = \frac{|\text{predicted} - \text{observed}|}{\text{observed}} \times 100\%

a

Calculate the percentage discrepancy between the Steady State model's prediction and the observed CMB temperature. [2]

b

Calculate the percentage discrepancy between the Big Bang model's prediction and the observed CMB temperature. [2]

c

Using your results from (a) and (b), evaluate which cosmological model is invalidated by the CMB evidence. Refer to the role of quantitative prediction in assessing scientific models. [2]

Solutions

16QuestionContinued expansion of universeAssessment Practice

6 marks~9 minCriterion D

Astronomers use ground-based telescopes to measure the redshift of light from distant galaxies. By comparing the observed wavelengths of spectral lines with laboratory reference values, they calculate how fast each galaxy is receding. These recession speeds provide key evidence for the ongoing expansion of the universe.

a

Explain how recession speed data supports the conclusion that the universe is expanding. [2]

b

Discuss two limitations of ground-based spectroscopy that reduce the reliability of redshift measurements. [2]

c

Evaluate the assumption that atomic spectral lines have remained unchanged over billions of years, and assess its impact on the reliability of recession speed calculations. [2]

Solutions

Astrophysics — Free MYP5 Physics Practice Questions