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  1. C

    Work w/ Pulleys

    So only the parallel component is responsible for doing the work, correct?
  2. C

    Work w/ Pulleys

    @Nathanael Ah, I think I was just making a stupid mistake. I was letting F = the force of gravity on the weight. Thanks for pointing that out.
  3. C

    Work w/ Pulleys

    Homework Statement A force F is used to raise a 4-kg mass M from the ground to a height of 5 m. What is the work done by the force F? (Note: sin60 = 0.87; cos60 = 0.5. Ignore friction and the weights of the pulleys.) A) 50 J B) 100 J C) 174 J D) 200 J Please click here for picture. Homework...
  4. C

    Arithmetic Question Involving Quantum Physics

    Homework Statement Two adjacent allowed energies of an electron in a one-dimensional box are 2.0 eV and 4.5 eV. What is the length of the box? Homework Equations E_n=\frac{h^2n^2}{8mL^2} The Attempt at a Solution My question is, since E_n and n^2 are both on separate sides of the equation...
  5. C

    Power in an AC Circuit

    So I can't use I^2R, because by definition the current would also be a different value for a new R? But we know the voltage will stay the same for a new R, so we can use V^2/R?
  6. C

    Power in an AC Circuit

    Homework Statement The average power dissipated by a resistor is 4.0 W. What is the average power if the resistance R is doubled? Homework Equations P_{rms}=I_{rms}^2R=I_{rms}V_{rms}=\frac{V_{rms}^2}{R} The Attempt at a Solution I am told the answer is 2.0 W. But here's what I am confused...
  7. C

    Radians v. Degrees

    Why would using degrees not give a unitless number?
  8. C

    Radians v. Degrees

    Homework Statement The voltage across a 60μF capacitor is described by the equation vC =(18 V) cos(200t), where t is in seconds. What is the voltage across the capacitor at t =0.010 s? Homework Equations N/A The Attempt at a Solution When you use degrees the answer is 18V and...
  9. C

    Bulb Brightness

    If I is the same for both resistors then according to P=I^2(R), R for the 60 W bulb must be higher. But I am confused because according to P = V^2/R the 60 W has a higher R...how do I know which equation to use?
  10. C

    Bulb Brightness

    Homework Statement Normally, household lightbulbs are connected in parallel to a power supply. Suppose a 40 W and a 60 W lightbulb are, instead, connected in series. (see here) Which bulb is brighter? Homework Equations P_{resistor}=I\Delta V=I^2R =\frac{(\Delta V)^2}{R} The Attempt at a...
  11. C

    Electrical Resistance (Easy Question)

    So if I'm not mistaken you can some them, \Sigma R = R_{muscle} + R_{fat} I think I can see why it would decrease now; just because more fat is being added doesn't make resistivity a bigger number. Fat was already present so the only number changing was A. Thanks guys.
  12. C

    Electrical Resistance (Easy Question)

    Homework Statement A person gains weight by adding fat - and therefore adding girth - to his body and his limbs, with the amount of muscle remaining constant. How will this affect the electrical resistance of his limbs? a. the resistance will stay the same b. the resistance will...
  13. C

    Slowing a Mass with a Spring Collision

    Oh I see, I was thinking the spring was starting from it's maximum amplitude, but it's not; it's starting at its eq. point. Thanks :)
  14. C

    Slowing a Mass with a Spring Collision

    Homework Statement A 1.5 kg mass slides across a horizontal, frictionless surface at a speed of 2.0 m/s until it collides with and sticks to the free end of a spring with spring constant 50 N/m. The spring's other end is anchored to the wall. How far has the spring compressed when the mass, at...
  15. C

    Acceleration of 3 Blocks w/ Pulley

    Homework Statement There's a picture with the problem attached A block with mass m = 1.5 kg hangs to the right of two blocks with masses m2 = 2.2 kg and m1 = 1.2 kg which sit on a table. All three blocks are connected with a string and pulley. Neglecting the mass of the pulley, string and any...
  16. C

    A Car Braking on a Road

    Oh my mistake, I didn't realize, but now that you guys explained it I can see the difference
  17. C

    A Car Braking on a Road

    It's from a practice test made by my prof., directly choice c reads "The equation for the stopping distance is 961 - 12d = 0"
  18. C

    A Car Braking on a Road

    Homework Statement The driver of a car at 31 m/s sees (t = 0, x = 0) an obstacle down the road and brakes. The car slows down with a constant deceleration which has a magnitude of 6 m/s^2. Select the correct statement below (let d = stopping distance, all units are SI) a. The position...
  19. C

    When can you assume dynamic equilibrium?

    I figured it out. I forgot to to remember that the kid is on an incline, but how I drew it is having the X-axis horizontal, therefore there will not be any acceleration along the Y-axis.
  20. C

    When can you assume dynamic equilibrium?

    SOLVED Homework Statement A 23 kg child goes down a straight slide inclined 38∘ above horizontal. The child is acted on by his weight, the normal force from the slide, and kinetic friction. Find the magnitude of the normal force. Homework Equations cos(theta)=adjacent/hypotenuse The...
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    Finding Absolute Uncertainty

    Homework Statement Hello, I have solved the problem, but not the way the writer intended. I need help figuring out how they wanted me to do it. Here's the problem: The circumference of a sphere is found to be 0.98 m +/- 0.01 m. Calculate the volume and absolute error with five digits...
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