Quantcast

Got Homework?

Connect with other students for help. It's a free community.

  • across
    MIT Grad Student
    Online now
  • laura*
    Helped 1,000 students
    Online now
  • Hero
    College Math Guru
    Online now

Here's the question you clicked on:

55 members online
  • 0 replying
  • 0 viewing

openstudyhelpplease Group Title

A certain radioactive element decays according to N=No e ^-kt. If 50% of the original element sample remains after 9 days, what is the decay rate?

  • one year ago
  • one year ago

  • This Question is Closed
  1. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    you know if \(t=9\) you have half of what you started with set \[e^{9k}=.5\] and solve for \(k\)

    • one year ago
  2. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    you got this? solve in two steps only

    • one year ago
  3. openstudyhelpplease Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    how do you solve for k?

    • one year ago
  4. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    1) write in equivalent logarithmic form (take the log) 2) divide by 9

    • one year ago
  5. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    \[e^{9k}=.5\iff 9k=\ln(.5)\iff k=\frac{\ln(.5)}{9}\]

    • one year ago
  6. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    then if you want a decimal, use a calculator

    • one year ago
  7. openstudyhelpplease Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    i have no idea what that means haha. so is it: k= .1831?

    • one year ago
  8. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    no

    • one year ago
  9. openstudyhelpplease Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    wait is ln the button on the calculator for e?

    • one year ago
  10. satellite73 Group Title
    Best Response
    You've already chosen the best response.
    Medals 2

    http://www.wolframalpha.com/input/?i=ln%28.5%29%2F9 usually \(ln\) is the button and \(e\) requires the shift key

    • one year ago
  11. openstudyhelpplease Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    ok, so i have to use the shift key right? i tried doing e ^.5 which was 1.64 and then divide that by 9 which was .1831

    • one year ago
  12. openstudyhelpplease Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    oh, the link helped. sorry we didn't learn this yet so I have no idea what im talking about

    • one year ago
  13. openstudyhelpplease Group Title
    Best Response
    You've already chosen the best response.
    Medals 0

    so the rate is k= -7.7 x 10 ^-2

    • one year ago
    • Attachments:

See more questions >>>

Your question is ready. Sign up for free to start getting answers.

spraguer (Moderator)
5 → View Detailed Profile

is replying to Can someone tell me what button the professor is hitting...

23

  • Teamwork 19 Teammate
  • Problem Solving 19 Hero
  • You have blocked this person.
  • ✔ You're a fan Checking fan status...

Thanks for being so helpful in mathematics. If you are getting quality help, make sure you spread the word about OpenStudy.

This is the testimonial you wrote.
You haven't written a testimonial for Owlfred.