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Assoli18 [71]
3 years ago
6

Brianna weighs 425 N. She climbs a flight of stairs to a height of 8 m. It takes her 6 seconds.

Physics
1 answer:
Aleks [24]3 years ago
5 0
<span>So we want to know how much work does Brianna do while climbing the stairs to a height h=8m while she weighs F=425N and in t=6s. So work W is defined as Force F times distance h or: W=F*h. Since Brianna has to use the force that is equal to her own weight during her climbing the calculation is this: W=F*h=425N * 8m=3400J. The work she does is W=3400 J.</span>
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Hansel pushes a 2 lb. box 5 feet in 20 seconds. How much work has he done?
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W = 2 x 5 = 10 foot-pounds of work

Foot-pounds are gross units. Better to work in SI units when you can!

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3 years ago
A 50-kg satellite circles the Earth in an orbit with a period of 120 min. What minimum energy is required to change the orbit to
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Answer: 2.94×10^8 J

Explanation:

Using the relation

T^2 = (4π^2/GMe) r^3

Where v= velocity

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Therefore,

T^2 = (0.9865 × 10^-13) × r^3

r^3 = 1/(0.9865 × 10^-13) ×T^2

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To find r1 and r2

T1 = 120min = 120*60 = 7200s

T2 = 180min = 180*60= 10800s

Therefore,

r1 = [(1.014 x 10^13)7200^2]^(1/3) = 8.07 x 10^6 m

r2 = [(1.014 x 10^13)10800^2]^(1/3) = 10.57 x 10^6 m

Required Mechanical energy

= - GMem/2 [1/r2 - 1/r1]

= (6.67 x 10^-11 x 6.0 x 10^24 * 50)/2 * [(1/8.07 × 10^-6 )- (1/10.57 × 10^-6)]

= (2001 x 10^7)/2 * (0.1239 - 0.0945)

= (1000.5 × 10^7) × 0.0294

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