Std 10th Science Part 1 – Chapter 10 : Space Missions Exercise Questions And Answers Maharashtra Board

Q1. Fill in the blanks and explain the statements with reasoning:

a. If the height of the orbit of a satellite from the earth surface is increased, the tangential velocity of the satellite will …

Answer – 

If the height of the orbit of a satellite from the earth surface is increased, the tangential velocity of the satellite will decrease.

Reasoning: The formula for the critical velocity (vc​) of a satellite is 

• Here, G (gravitational constant), M (Earth’s mass), and R (Earth’s radius) are constant.
• The critical velocity is inversely proportional to the square root of the orbital radius (R+h).
• As the height (h) increases, the denominator increases, and thus the velocity (vc​) must decrease.

b. The initial velocity (during launching) of the Managalyaan, must be greater than …………..of the earth.

Answer – 

The initial velocity (during launching) of the Managalyaan, must be greater than escape velocity of the earth.

• Reasoning: Escape velocity is the minimum velocity required for an object to escape the gravitational influence of the Earth and travel into outer space. Since Mangalyaan (Mars Orbiter Mission) was sent away from the Earth to Mars, its initial velocity had to be greater than the Earth’s escape velocity, which is 11.2 km/s.

Q2. State with reasons whether the following sentences are true or false 

a. If a spacecraft has to be sent away from the influence of earth’s gravitational field, its velocity must be less than the escape velocity.

Answer – 

• False.
• Reason: To escape the Earth’s gravity, the moving object’s initial velocity must be greater than or equal to the escape velocity. If the velocity were less than the escape velocity, the spacecraft would eventually fall back to Earth.

b. The escape velocity on the moon is less than that on the earth.

Answer –

• True 
• Reason: Escape velocity depends on the mass (M) and radius (R) of the planet/object (v_esc​= √2GM​​ / R). The Moon has a significantly smaller mass and radius compared to the Earth, which results in a smaller escape velocity.

c. A satellite needs a specific velocity to revolve in a specific orbit.

Answer –

• True.
• Reason: For a satellite to stay in a stable orbit at a specific height, it must be given a precise tangential velocity known as the critical velocity (vc​). This velocity is required to provide the exact centripetal force needed to balance the Earth’s gravitational pull.

d. If the height of the orbit of a satellite increases, its velocity must also increase.

Answer –

• False.
• Reason: As shown by v_c​= √GM / R+h​​, the critical velocity is inversely related to the orbital radius. If the height (h) increases, the orbital radius (R+h) increases, causing the critical velocity of the satellite to decrease.

Q3. Answer the following questions:

a. What is meant by an artificial satellite? How are the satellites classified based on their functions?

Answer –

• Artificial Satellite: A man-made object that revolves around the Earth or any other planet in a fixed orbit. They typically use solar energy and carry instruments to receive and transmit signals.
• Classification by Function:
  • Weather Satellite: For studying and predicting weather.
  • Communication Satellite: For establishing communication globally (e.g., telephone, internet).
  • Broadcast Satellite: For telecasting television programs.
  • Navigational Satellite: For accurately fixing the location (latitude and longitude) of a place (e.g., IRNSS).
  • Earth Observation Satellite (Remote Sensing): For studying Earth’s surface (forests, oceans, minerals) and managing natural calamities.
  • Military Satellite: For security and collecting information about the enemy.

b. What is meant by the orbit of a satellite? On what basis and how are the orbits of artificial satellites classified?

Answer –

• Orbit of a Satellite: The fixed path (circular or elliptical) in which a satellite revolves around the Earth.
• Classification Basis: Orbits are primarily classified based on their height from the Earth’s surface.

• Orbit Classification:
  1. Low Earth Orbits (LEO): 180 km to 2000 km height. Used for scientific experiments and atmospheric studies. Revolution time is around 90 minutes.
  2. Medium Earth Orbits (MEO): 2000 km to 35780 km height. Used for polar studies and navigation (e.g., GPS satellites).
  3. High Earth Orbits (HEO): > 35780 km height. Includes
     Geosynchronous Satellites which appear stationary relative to Earth, used for meteorology and communication.

c. Why are geostationary satellites not useful for studies of polar regions?

Answer –

• Geostationary satellites revolve in orbits parallel to the equator.
• Because their revolution time is 24 hours (matching Earth’s rotation) in this equatorial orbit, they appear stationary relative to a specific portion of the Earth.

Therefore, they can continuously observe only the region directly above the equator, making them unable to observe or study the North or South polar regions.

d. What is meant by satellite launch vehicles? Explain a satellite launch vehicle developed by ISRO with the help of a schematic diagram.

Answer –

• Satellite Launch Vehicles: These are machines used to place artificial satellites into their specific orbits. Their function is based on Newton’s Third Law of Motion (thrust from expelled gas propels the vehicle).

• ISRO Launch Vehicle (PSLV or GSLV): ISRO developed launch vehicles like the PSLV (Polar Satellite Launch Vehicle).
  • Structure/Working: They are usually made of multiple stages to reduce weight step-by-step during launch.
    1. The first stage (using solid fuel) provides the initial thrust. Once the fuel is used up, the empty tank and engine are detached and fall away.
    2. The next stage ignites, and since the overall weight of the vehicle is now reduced, it can achieve a higher speed, continuing to push the remaining stages and the satellite towards the required orbit.

e. Why it is beneficial to use satellite launch vehicles made of more than one stage?

Answer –

• The major portion of a launch vehicle’s total weight is the
  fuel.
• Using multi-stage vehicles is beneficial because it allows the weight of the vehicle to be reduced step-by-step after launching.

When a stage’s fuel is exhausted, the empty part is detached. This reduction in weight allows the remaining stages to move with a higher acceleration/speed, making it easier and more efficient to reach the required orbit.

Q4. Complete the following table.

Answer – 

Q5. Solve the following problems.

a. If mass of a planet is eight times the mass of the earth and its radius is twice the radius of the earth, what will be the escape velocity for that planet?

Answer – 

Given:

• Earth’s escape velocity (v_esc,E​) ≈ 11.2 km/s.
• Planet’s mass (M_P​) = 8 × M_E​
• Planet’s radius (R_P​) = 2 × R_E​

Calculation: v_esc,P ​= 2 × v_{esc ,E}​ = 2×11.2 km/s = 22.4 km/s

Answer: The escape velocity for that planet will be 22.4 km/s.

b. How much time a satellite in an orbit at height 35780 km above earth’s surface would take, if the mass of the earth would have been four times its original mass?

Answer – 

• Given:
  • Original Earth’s mass (M_E,old​) → New Earth’s mass (M_E,new​) =4M_E,old​.
  • Original revolution time (T_old​) for h=35780 km is 24 hours (Geosynchronous orbit).
  • The radius of the orbit (r=R+h) is constant.

Answer : The satellite would take 12 hours for one revolution.