Howardites

A printable worksheet for the lesson Gravitational fields and escape (A-level). It prints on A4 without the website around it. The answers are on a separate sheet for the teacher.

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A-level · Ages 16 to 18 (Years 12 and 13)Howardites worksheet

Gravitational fields and escape

Name:Class:Date:

Key words

Vesta
The second-largest object in the asteroid belt and the likely home of the howardite, eucrite and diogenite meteorites.
Escape velocity
Escape velocity is the speed an object needs to break free of a body's gravity without further push.
Spallation
Spallation is the splitting off of fragments, either of rock near an impact or of atomic nuclei struck by cosmic rays.
Martian meteorite
A rock that was blasted off Mars by an impact and later landed on Earth.
Plagioclase
A feldspar mineral, rich in calcium or sodium, that forms the pale grains in many achondrites and lunar rocks.
Maskelynite
Plagioclase feldspar turned into glass by intense shock, while keeping the shape of the original crystals.

Choose the right answer

Circle the letter of the right answer.

  1. What is the gravitational potential at the surface of Mars? (GM = 4.28 × 10¹³ m³ s⁻², r = 3.39 × 10⁶ m)
    • AAbout −1.3 × 10⁷ J kg⁻¹
    • BAbout −2.5 × 10⁷ J kg⁻¹
    • CZero, because potential is measured from the surface
    • DAbout −3.7 N kg⁻¹
  2. Which list puts these bodies in order of escape velocity, lowest first?
    • AVesta, Mars, Moon, Earth
    • BVesta, Moon, Mars, Earth
    • CMoon, Mars, Vesta, Earth
    • DMoon, Vesta, Mars, Earth
  3. What is the minimum kinetic energy a 2.0 kg rock needs to escape from Mars, where the escape velocity is 5.0 km s⁻¹?
    • A2.5 × 10⁷ J
    • B1.3 × 10⁷ J
    • C5,000 J
    • D5.0 × 10⁷ J
  4. Why could a large impact on Vesta send so much of its crust into space?
    • AIts fast spin flings loose rock into space
    • BIts atmosphere carries debris upwards
    • CIts crust is far less dense than other rock
    • DEjecta need only about 360 m s⁻¹ to escape
  5. Why was it long thought impossible for rocks from Mars to reach Earth?
    • AMars was thought to have a higher escape velocity than Earth
    • BImpacts on Mars were thought to be too rare
    • CAccelerating rock to 5 km s⁻¹ was expected to melt it
    • DRocks were thought unable to cross the asteroid belt

True or false?

Is the answer given right? Tick True or False.

  1. A rock leaves Vesta's surface at 300 m s⁻¹, below its escape velocity of 362 m s⁻¹. Ignoring other bodies, what happens to it?

    Answer given: It cannot escape: its kinetic energy is less than GMm/r TrueFalse

  2. Roughly how many times stronger is the gravitational field at Earth's surface than at Vesta's?

    Answer given: About 40 times TrueFalse

Write your answer

Answer in a word or a short sentence.

  1. A 1 g pebble and a 1 t boulder lie side by side on Mars. Which quantity is the same for both?
  2. Which two features make launching rock into space far harder from Venus than from Mars?
  3. A student calculates Vesta's escape velocity as 1.31 × 10⁵ m s⁻¹. Which step have they missed?

Task

Calculate the escape velocity of the Moon (M = 7.35 × 10²² kg, r = 1.74 × 10⁶ m) and of Mars (M = 6.42 × 10²³ kg, r = 3.39 × 10⁶ m). Then plot escape velocity against radius for Vesta, the Moon, Mars and Earth (M = 5.97 × 10²⁴ kg, r = 6.37 × 10⁶ m) and comment on the trend.

Howardites · free to copy for use in your classroom · answers are on the separate teacher's answer sheet