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November 1, 2014

Homework Help: physics

Posted by Levi B. on Friday, January 20, 2012 at 6:55pm.

A de-orbit burn, similar to that presented in the previous math problem, has been performed. During this de-orbit burn a pre-calculated ∆V (delta V, change in velocity) of 290 ft/s (or 88.4 m/s) will be used to decrease the Shuttle’s altitude from 205 miles to 60 miles at perigee.The Shuttle’s Orbital Maneuvering System (OMS) engines provide a combined thrust of 12,000 force-pounds or 53,000 Newtons.The Shuttle weighs 2.50 x 105 lbs when fully loaded. The Shuttle has a mass of 1.13 x 105 kg when fully loaded.
A little background: What is the difference between the Shuttle’s mass and weight? An object’s mass does not change from place to place, but an object’s weight does change as it moves to a place with a different gravitational potential. For example, an object on the moon has the same mass it had while on the Earth but the object will weigh less on the moon due to the moon’s decreased gravitational potential.The shuttle always has the same mass but will weigh less while in orbit than it does while on Earth’s surface.
Calculate how long a de-orbit burn must last in minutes and seconds to achieve the Shuttle’s change in altitude from 205 miles to 60 miles at perigee.Use the equations and conversions provided below in method 1 or method 2 to find the required burn time.Please report your answer in minutes and seconds by converting your partial minutes into seconds.For example, if your answer is 92 seconds, convert to minutes by multiplying your answer by 1min/60 seconds to get 1.5333 minutes. Then take the 0.53333 minutes and convert into seconds by multiplying by 60 seconds per minute to get 32 seconds. Your reported quantity would be 1 minute and 32 seconds.
Method 1: F = ma Newton’s Second Law, where:
a, acceleration is in meters per second per second (m/s2)units
F, force is in Newtons (1 N = 1kg m/s2 )
M, mass is in kg units
a = ∆V/ t Equation that defines average acceleration, the amount by
which velocity will change in a given amount of time.
t = ∆V/a Rearranging the acceleration equation above to find the
time required for a specific velocity change given a
specific acceleration, where:
∆V is change in velocity in meters per second (mps)
a, acceleration is in meters per second per second, m/s2
t, required time in seconds
OR USE,
Method 2: F = Wa, where:
a, acceleration is in units of g’s (1g is equal to 32 feet
per second per second, ft/s2)
F, force is in force pound units
W, weight is in units of pounds
a = ∆V/ tEquation that defines average acceleration, the average
amount by which velocity will change in a given amount
of time.
t = ∆V/a Rearranging the acceleration equation above to find the
time required for a specific velocity change given a
specific acceleration, where:
∆V is change in velocity in feet per second (ft/s)
a, acceleration is in feet per second per second units
t, required time in seconds

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