Man jumps on moving wagon

  • #1
AndrewMorris
4
1
Homework Statement:
My daughter was asked this question:
A person of mass 60 kg running at 8 m/s reaches a wagon of mass 80 kg going at 2 m/s and jumps onto it. Calculate the velocity of the wagon immediately after the person jumps on.
Relevant Equations:
total momentum before impact = total momentum after impact
Using conservation of momentum I would say (60 x 8) + (80 x 2) = (60 + 80) v
so v = 400/140 = 2.86 m/s.
However, this is not one of the multiple choice responses. What am I doing wrong?
 

Answers and Replies

  • #2
TSny
Homework Helper
Gold Member
13,851
4,021
Setup looks right. But check the number 400.
 
  • #3
Orodruin
Staff Emeritus
Science Advisor
Homework Helper
Insights Author
Gold Member
20,004
10,650
Apart from that, consider using symbolic calculations and only insert your numbers at the end. It often avoids this kind of mistakes. Or at least use units throughout.
 
  • #4
AndrewMorris
4
1
oh man, I used to be good at maths, honest. Thanks :-)
 
  • #5
TSny
Homework Helper
Gold Member
13,851
4,021
oh man, I used to be good at maths, honest. Thanks :-)
It was just a careless error. Happens to us all :oldsmile:
 

Suggested for: Man jumps on moving wagon

Replies
2
Views
430
Replies
1
Views
159
Replies
11
Views
584
Replies
11
Views
416
  • Last Post
Replies
8
Views
714
Replies
38
Views
160
Replies
24
Views
494
Replies
12
Views
723
Top