A spacecraft moves in a circular orbit with a speed of 7.77 km/s with a period of 88.9 min. What is the radius of the spacecraft's orbit? what is the radial acceleration of the satellite?

Then, in order to begin its re-entry, the spacecraft engines are fired to provide an acceleration of 5.20 m/s2 in a direction opposite to its velocity. What is the magnitude of the spacecraft's total acceleration just after the engines begin to fire.

hmm... can someone explain me how to solve this problem?

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