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: Forces, velocities and angles

  1. Oct 29, 2006 #1
    I have a take home quiz for my physics class. Out of the 10 questions I have answered 7 of them, whether they are right I don't know. First and foremost I need help on the ones I haven't solved yet. I am not necessarily looking for someone to give me the answers, but rather help me setup the problem and use formulas to arrive at the answer myself.

    The hardest question is #3.

    A 200lb man stands tiptoed on one foot so that all his weight is borne by the ground beneath the ball of the foot. If the foot and ankle are considered as an isolated body, the three forces that are in equilibrium are the reaction W of the ground, the pull T of the achillies tendon and the compression C of the tibia. The force C is downward at an angle 15* from vertical. The force T is upward at 21* from the vertical. W is an upward force of 200lbs. Calculate the values of C and T. (HInt: one way to do this is to have two simultaneous equations, one balancing the horizontal components of force and the other balancing the vertical components. Another way is to use the law of sines)


    A rocket exhausts fule with a velocity of 1500m/s, relative to the rocket. It starts from rest in outer space with the fuel comprising 80% of the total mass. When all the fuel has been exhausted, what is the rockets speed?


    A car rounds a 75m radius curve at a constant speed of 18m/s. A ball is suspended by a string from the ceiling of the car and moves with the car. What is the angle between the string and the vertical (y-axis)?
  2. jcsd
  3. Oct 30, 2006 #2


    User Avatar
    Science Advisor

    If this is a take home TEST, are you allowed to seek help from others? If that is true then I see no point in the test at all.
  4. Oct 31, 2006 #3
    Yes, it is open book open notes. We are allowed to seek help too. He wants us to understand the concepts and apply them, even if we are aided, rather than stay confused and not know what we are doing.
  5. Oct 31, 2006 #4
    well for problem three he basically tells you how to do it: it's a vector math problem. You want to take the x and y components of the C and T vectors and set them equal to the W (normal) force

    something like:
    C cos(theta1) + T cos(theta2) = 0
    C sin(theta1) + T sin(theta2) = 200lbs
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook