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posted by  Kathia on 11/7/2009 5:47:04 AM  |  status: Live  |  Earned Karma: 0

PHYSICS (PHY101)

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General Physics PHYSICS (PHY101) by Virtual University 12 1 11/8/2009 at 5:00:00 PM
Question Details:
 

Q 1

If two particles have equal kinetic energies, are their momenta necessarily equal? Explain.                                                                                                                                                       

Q 2

Where is the center of mass of Earth's atmosphere?                                              

Q 3

An airplane propeller is rotating at 1900 rev/min.Compute the propeller's angular velocity in rad/s.                                                                                                                    

Q 4

Two ice dancers are at rest on the ice, facing each other with their hands together. They push off on each other in order to set each other in motion. The subsequent momentum change (magnitude only) of the two skaters will be ____. Also write it’s (the answer you choose) detail reason.                                                                                              

A. greatest for the skater who is pushed upon with the greatest force

B. greatest for the skater who pushes with the greatest force

C. the same for each skater

D. greatest for the skater with the most mass

E. greatest for the skater with the least mass                

Q 5

How much work is done by an applied force to lift a 20-Newton block 2.0 meters vertically at a constant speed?                                                                                 

Q 6

A student with a mass of 50.0 kg runs up three flights of stairs in 10.0 sec. The student has gone a vertical distance of 8.0 m. Determine the amount of work done by the student to elevate his body to this height. Assume that her speed is constant.                  

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posted by Tours2009 on 11/7/2009 10:55:42 PM  |  status: Live
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Response Details:
Question 4:
Answer: C In this situation, the force on the first ice dancer is the same as the force on the second ice dancer (Newton's third law of motion). And these forces act for the same amount of time to cause equal impulses on each skater. Since impulse is equal to momentum change, both skaters must also have equal momentum changes. The mass of the individual skaters will only effect the subsequent velocity change.
Question 5:
 To lift a 20-Newton block at constant speed, 20-N of force must be applied to it (Newton's laws). Thus, W = (20 N) * (2 m) * cos (0 degrees) = 40 Joules 
Question 6:
 

The student weighs 490 N (Fgrav= 50 kg * 9.8 m/s/s).

To lift a 490-Newton person at constant speed, 490 N of force must be applied to it (Newton's laws). The force is up, the displacement is up, and so the angle theta in the work equation is 0 degrees. Thus,

W = (490 N) * (8 m) * cos (0 degrees) = 3920 Joules

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