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: Earth impacted?

  1. Oct 12, 2015 #1
    1. The problem statement, all variables and given/known data

    Most geologists believe that the dinosaurs became extinct 65 million years ago when a large comet or asteroid struck the earth, throwing up so much dust that the sun was blocked out for a period of many months. Suppose an asteroid with a diameter of 2.0km and a mass of 1.3*10^13 kg hits the earth with an impact speed of 4.2*10^4 m/s.

    a) What is the earth's recoil speed after such a collision? (Use a reference frame in which the earth was initially at rest.)

    b) What percentage is this of the earth's speed around the sun?

    2. Relevant equations
    I used the law of conservation of momentum (Pf = Pi) This states that the total momentum after an interaction is equal to the total momentum before the interaction.

    3. The attempt at a solution
    a) Using Pf=Pi, I solved for the final velocity, which is the same for both the earth and the asteroid, and got 668.896 m/s. (The final velocity is the earth's recoil speed)

    b) NOW for this part, I got from my textbook that the "earth's mean distance from sun (m) = 1.50*10^11 m. Also, I got that the earth's period (years) = 1.00 years

    Using these, I found the speed to be 4756.468798 m/s by converting years to seconds and dividing the two numbers (to get m/s)


    (668.896m/s / 4756.4688798m/s) * 100% = 14%

    Did I do this correctly? Did I use the correct numbers from my textbook to get the speed?

    Please help!

  2. jcsd
  3. Oct 12, 2015 #2


    User Avatar
    Homework Helper
    Gold Member

    Hello @Dick Channy,

    Welcome to Physics Forums! :smile:

    I got something many orders of magnitude different.

    Please show your work on that one. (Your approach of using conservation of momentum is correct though -- something must have gone wrong with the arithmetic.)

    Don't forget that the circumference of a circle is [itex] 2 \pi [/itex] times the radius.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted