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: Largest mass of rock that wont sink the boat

  1. Oct 4, 2008 #1
    1. The problem statement, all variables and given/known data
    You begin by measuring one of the hemispheres, finding that it has a mass of 21 g and a diameter of 8.6 cm

    Basically you have a hemisphere shaped boat with mass 21g and diamter 8.6cm you have to find the heaviest mass of rock that u can put in the boat that wont sink it.

    What is the mass of the heaviest rock that, in perfectly still water, won't sink the plastic boat?

    2. Relevant equations

    I equated the densities of the boat and water and solved for m

    3. The attempt at a solution
    I got 3.85kg as an answer
  2. jcsd
  3. Oct 4, 2008 #2
    I assume that this answer is wrong, that's why you're posting here. Am I right?
    It would help if you posted your method to aquire your answer, aswell as all the relevant values ie. densities.
  4. May 5, 2009 #3
    I'm on a similar problem. The text book appears to say that I should try to set the average density of the sphere equal to the density of the water. So, I tried:
    rou(ave)=[mass(sphere)+mass(rock)+mass(air in sphere)]/volume
    Then I set the two equal to each other and solved for the mass of the rock. I've gone through it several times and can't come up with the correct answer.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook