Momentum, Impulse, and Collision

  • Thread starter Tastosis
  • Start date
  • #1
Tastosis
32
0

Homework Statement


Two skaters stand in the center of a circular rink of frictionless ice. When the skaters push on one another, they move apart along the same straight line. If the skater of mass m1 = 50 kg reaches the edge of the rink after 12 seconds and the other skater reaches the opposite edge of the rink in 18 seconds, what is the mass m2 of the second skater?


Homework Equations


M1V1 + M2V1 = M1V2 + M2V2 ?


The Attempt at a Solution


How do I get the mass if the distance is not given?
 

Answers and Replies

  • #2
ehild
Homework Helper
15,543
1,915
They traveled the same distance.Find the ratio of the speeds.

ehild
 
  • #3
Tastosis
32
0
I'm confused >.<

So the equation I'm using is wrong?
 
  • #4
ashishsinghal
462
0
no there is no problem with the equation.
let the distance moved be x and then solve. It will get cancelled.
 
  • #5
Tastosis
32
0
50kg * x/12s+ M2 * x/18s = 50kg * x/12s + M2 * x/18s ?
 
  • #6
ehild
Homework Helper
15,543
1,915
I'm confused >.<

So the equation I'm using is wrong?

It is not wrong, only it does not mean anything. Both sides are identical, so you say that something is equal with itself. What did you want to state with that equation?

ehild
 
  • #7
Tastosis
32
0
50kg (1/12s) + M2 (1/18s) = 0

M2 = [50kg (1/12s)] / 1/18s

M2 = 75kg

Did I do it right?
 
  • #8
ehild
Homework Helper
15,543
1,915
50kg (1/12s) + M2 (1/18s) = 0

M2 = [50kg (1/12s)] / 1/18s

M2 = 75kg

Did I do it right?

You made two mistakes and they canceled each other resulting in a correct mass. Your equation would result in a negative mass.

The skaters moved in opposite directions, one velocity is positive, the other is negative. So the correct equation is

m1 x/12 - m2 x/18 =0

Solving the equation correctly,

m1/12 = m2/18 , m2=m1 18/12 = 75 kg.

ehild
 
  • #9
Rayquesto
318
0
do we also have to consider the initial velocity and the amount of force pushed in a given time interval of 6 seconds?
 
  • #10
ehild
Homework Helper
15,543
1,915
I do not get you. There is no question concerning the force between the skaters, setting them to move. It is assumed in such problems that the force acts for a very short time so the skaters are still very near to their original position when they are separated and move with some velocity. The difference between the times reaching the plank (6 s) comes from the different speeds the skaters move.


ehild
 
  • #11
Rayquesto
318
0
I was referring to the fact that Force times Time differenc is equal to the change in momentum. So, maybe you need to find initial velocity through that.
 
  • #12
ehild
Homework Helper
15,543
1,915
I was referring to the fact that Force times Time differenc is equal to the change in momentum. So, maybe you need to find initial velocity through that.

Read the problem: "Two skaters stand in the center of a circular rink" What is the initial velocity?

ehild
 
  • #13
Rayquesto
318
0
Orginially I got 75 kg doing exactly what everyone else is doing, but I tried considering their small force. I know the answer is 75kg but I'm still skeptical about how like a reverse impulse can be tied into. that\s how my mind works though. I try to consider everything, but I still think the answer is 75 kg regaurdless of my skeptics.
 

Suggested for: Momentum, Impulse, and Collision

Replies
6
Views
378
Replies
23
Views
349
Replies
10
Views
577
Replies
3
Views
385
  • Last Post
Replies
14
Views
598
Replies
17
Views
2K
Replies
3
Views
461
Replies
16
Views
847
Replies
32
Views
257
Replies
9
Views
692
Top