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Q.45 - Excercises And Problems

Physics for Scientists and Engineers: A Strategic Approach with Modern Physics
Found in: Page 355

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Short Answer

An astronaut circling the earth at an altitude of is horrified to discover that a cloud of space debris is moving in the exact same orbit as his spacecraft, but in the opposite direction. The astronaut detects the debris when it is away. How much time does he have to fire his rockets and change orbits?

The time required to fire his rockets and change orbits is

See the step by step solution

Step by Step Solution

Step 1: Given information

height of the astronaut

Gravitational constant

Radius of earth

distance between debris and astronaut

Step 2: Explanation

One of the essential concepts to solve this problem is the utilization of the equations of centripetal and gravitational force.

From them it will be possible to find the speed of the body with which the estimated time can be calculated through the kinematic equations of motion. At the same time for the calculation of this speed it is necessary to clarify that this will remain twice the ship, because as we know by relativity, when moving in the same magnitude but in the opposite direction, with respect to the ship the debris will be double speed.

By equilibrium the centrifugal force and the gravitational force are equal therefore


is mass spacecraft

is velocity

is Gravitational Universal Constant

is Mass of earth

Radius of earth and orbit

Re-arrange to find the velocity

Replacing with our values we have

From the cinematic equations of motion we have to

Remember that the speed is double for the counter-direction of the trajectories.


Therefore the time required is

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