1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Homework Help: Who wants to grade my test? (physics 1, simple for physics buffs)

  1. Feb 20, 2008 #1
    Just took my 2nd physics test of the semester. didn't do so well on the first one, so i'm kind of anxious to see how i did on this one(our professor lets us keep the test and we turn in the scantron sheet). honestly, i have no clue how well i did. i know its a lot to ask, but if anyone wants to figure some of these answers out that would be great. i bolded the answers that i got. THANKS IN ADVANCE!!

    1) A small body is suspended from the inside of the roof of a car which travels at a constant speed. If the body is found suddenly to til towards the front of the car, the car has:
    (a) turned to the left
    (b) decreased speed
    (c) unchanged speed
    (d) increased speed
    (e) turned to the right

    2) A constant net force, Fnet, acts on a body of mass, m, and produces an acceleration of a. If an additional force, F1, is applied to this body and the resulting force produces an acceleration of 2/5a, then F1 is equal to:
    (a) -7/5 Fnet
    (b) 3/5 Fnet
    (c) -3/5 Fnet
    (d) 7/5 Fnet
    (e) 2/5 Fnet

    3) A verticle force, Fp, is applied to a body of mass, m = 8.47 kg. This force causes the body to undergo an upward acceleration, a = 2.64 m/s^2. The magnitude of Fp is:
    (a) 116 N
    (b) 68.3 N
    (c) 32.7 N
    (d) 22.2 N
    (e) 105 N

    4) A body of weight, W, rests on a scale, which is placed on the floor of an elevator. The scale shows the apparent weight of this body to be 0.700 W. Which of the following statements is correct?:
    (a) Elevator is accelerating downwards w/ an acceleration of 0.300g
    (b) Elevator is moving downwards with an acceleration of 0.700g
    (c) Elevator is either at rest or moving up/down at constant speed
    (d) Elevator is at rest
    (e) Elevator is accelerating upwards with an acceleration of 1.70g

    5) The system shown is pushed to the right by an applied force, Fp, as shown, causing the system to accelerate at a constant rate, a. No other forces, including frictional forces, act on this system. The net force acting on the body of mass, 3m, is:

    -----Fp-----> (4 M) (3 M)

    (a) 3/4 Fp
    (b) 3/7 Fp
    (c) -4/3 Fp
    (d) -3/7 Fp
    (e) 4/7 Fp

    6) A force, Fp, is applied to a body, where Fp= 27.2 N, angle= 31.8, and m= 4.17kg. The coefficient of kinetic friction between the body and the surface is 0.294. The acceleration of this body is:
    (a) 2.57 m/s^2
    (b) 2.66 m/s^2
    (c) 3.53 m/s^2
    (d) 3.67 m/s^2
    (e) 2.45 m/s^2

    7) A body of mass, 4.50 kg, moves on a level frictionless surface. A horizontal force, F, acts on this mass, which accelerates at a rate of 5.00 m/s^2. When another body of mass, m, is placed on top of the first body and the same force is applied, the combination accelerates at 3.00 m/s^2. The value of the mass, m, of the body that was placed on the 4.50 kg body was:
    (a) 6.00 kg
    (b) 8.00 kg
    (c) 6.50 kg
    (d) 3.00 kg
    (e) 2.33 kg

    8) Two individuals are pulling on opposite ends of a rope. The forces exerted by each individual has a magnitude, F. The tension in the rope is:
    (a) 0
    (b) F^2
    (c) F
    (d) F/2
    (e) 2F

    9) A body rests on a place. The plane is slowly tilted until the body slides down the plane with a constant velocity. At this time the plane makes an angle to the horizontal of 18.7 degrees. The coefficient of kinetic friction between the body and the plane is:
    (a) 0.482
    (b) 0.437
    (c) 0.409
    (d) 0.338
    (e) 0.326

    10) A body is attached to a cord the length of 1.57m and is whirled in a circle, one end of the cord being held fixed at the center of the circle. The tangential speed of this body is constant and equal to 6.14 m/s. How many revolutions does the body perform in 12.5 seconds?:
    (a) 7.78
    (b) 8.27
    (c) 4.14
    (d) 6.71
    (e) 5.82

    11) A car travels at a constant speed, v, around an unbanked curve of radius, r=93.6m. The coefficient of static friction between the tires of the car and the surface of the road is 0.407. The maximum speed of the car, for which the wheels will not slip is:
    (a) 21.7 m/s
    (b) 19.3 m/s
    (c) 20.4 m/s
    (d) 16.5 m/s
    (e) 18.1 m/s

    12) A body of mass, m= 1.48kg, is attached to a cord of length 1.58m and moves in a horizontal circular loop at constant speed, v. The tension in the cord is 23.6 N. The value of v is:
    (a) 4.55 m/s
    (b) 7.74 m/s
    (c) 5.79 m/s
    (d) 5.02 m/s
    (e) 5.47 m/s
  2. jcsd
  3. Feb 20, 2008 #2
    p.s.- I can try to tell you how i got each answer if you'd like. I bolded my answers to show that this isn't a homework assignment and that I got these answers already. thanks
  4. Feb 20, 2008 #3
    2 c f_net + F_1 = 2/5
    3 d or possibly e if we have to allow for gravity if it isn't already included in F_p
    4 a surely the scale will measure W if the elevator is at rest
    5 b For both masses you have f=m.a a is the same. the rest is algebra.
    6 ? can't make out the exact direction of the force from your description
    8 c suppose one of them ties the rope to something. what would the tension be, why would it be different?
    the rest is OK. So I think you have 5, maybe 6 mistakes
    You seem to be doing OK with rotation and the centripetal force, but not good with accelerations, and the addition of forces
  5. Feb 20, 2008 #4
    bump. anyone else?
  6. Feb 21, 2008 #5
    I can look at it come weekend, but not not until then.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook