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Homework Help: Please help me with my son's physics problems!

  1. Jun 3, 2012 #1
    First of all I have been searching everywhere over the internet for help. My son is asking me for help with his physics home problems and I want to teach him but I don't know how to solve any of these could someone please help me and solve these and post how the solved them and what equations they used?
    1) A box weighing 210 N is pushed up an incline plane that is 3.0 meters long. A force of 140 N is required. If the box is lifted 1.0 m, what is the efficiency of the inclined plane?

    2) A figure skater with arms drawn spins on the ice at a rate of 5.0 rad/s and has a moment of inertia of 1.875 kg*m^2 . What is the angular momentum of the skater?

    3) A 1,500kg truck moving at 15 m/s strikes a 750 kg automobile stopped at a traffic light the vehicle. The vehicles hook bumpers and skid together at 10 m/s. What is the decrease in kinetic energy?
    4) A uniform bridge span weighs 50,000 N is 40 m long. An automobile weighing 15,000 N is parked with its center of gravity located 12 m from the right pier. What upward support force is provided by the left pier?

    5) A 61 kg student sits at a desk 1.25m away from a 70 kg student. What is the magnitude of the gravitational force between the two students?

    6) A tire has an initial angular velocity of 8∏ (pi) rad/s and slows at a rate of 2 rad/s. What is the angular displacement as it comes to a stop?

    7) A rubber stopper of mass m2 = 0.020 kg is tied to a string an allowed to revolve in a circle of radius of 0.95 m. There is a mass of m1 = 1.00 kg hanging from the bottom providing a centripetal force. Calculate the linear (tangential) speed of the rubber stopper.

    8) A rollercoaster car speeds up and down a hill past points a, b, and c as shown. The car has a mass of 500 kg and a speed of 25.0 m/s at point B where the track radius is 10 m. A: What is the maximum speed the car can have at point c, radius 19.6 m, for the gravitational force to hold it on the track? Use g = 10.0 m/s^2

    9) On the planet Xenos, an astronaut observes that a seconds pendulum with a mass of 2.0 kg and a length of 1.216m oscillates with a period of 2.00 seconds. What is the free-fall acceleration on the planet xenos?
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jun 3, 2012 #2


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    Science Advisor
    Gold Member

    Hi spartankaboos. The procedure at PF for getting help is listed in the Rules tab. Have your son open one thread for each problem that he has started, and have him show his work (attempt at a solution). He must fill out the headings in the form, they are mandatory--not optional. Then someone can help him.

    As for helping him yourself, it goes without saying that you must understand the material first. I suggest that you read his textbook before attempting the problems. It is not sufficient to just plug numbers into an equation, because you will be unable to explain the reasoning behind the solution, or answer questions that your son will (should) ask. If you want assistance from PF for your own work, then post your own thread. You, too, must show your work before you receive assistance.
    Last edited: Jun 3, 2012
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