Find magnitude, help

  • Thread starter nasadall
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  • #1
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Homework Statement



A ball of mass 350g is travelling with a speed of 4m/s when it hits at right angles a fixed vertical wall. The ball rebounds with a speed of 3m/s. Find the magnitude of the impulse exerted by the ball on the wall. Using a simple diagram show the direction of velocities and the impulse.

Homework Equations



m = 350g or m = 0.35kg v1 = - 4m/s^-1 v2 = 3m/s^-1

Magnitude = mv2 – mv1

The Attempt at a Solution



Magnitude = 0.35 3 – 0.35(- 4)

Magnitude = 1.05 – 1.4

Magnitude = - 0.35



Hi can some one check this equation for me please.

Also is there a unit to simbolize magnitude? and is the final answer 0.35 given in joules???

Last one how would i draw a simple diagram showing the direction of velocities and the impulse???

thank you
 

Answers and Replies

  • #2
114
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Your final value is correct.
However, being a magnitude , it should have positive sign.

As for the units, just work them out by what you have in the equation.
I'm sure you know the units of m and v (and you're given them, anyway), so just use those.

Start drawing a diagram showing the velocities only, I'm sure you'll understand in what direction should the impulse go.
 
  • #3
28
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i've calculated wrong.
it should have been.

Magnitude = 1.05-(-1.4)
= 2.45

2.45 is the final answer.

kg m/s

is the final answer given in N??
 
  • #4
114
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N is kg m/s2, but you only have kg m/s.

So you can either leave it as kg m/s or rewrite it as..?
 
  • #5
28
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thank you for you help, but i can't get there, to be honest, i started studying after 15 years and this thing is doing my head, i have to handle my course work tomorroy, and i'm still half way.lollol
 
  • #6
114
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Just look at how the RHS of the two equations below is altered and you will know how to change the LHS as well.

N = kg m/s^2

? = kg m/s
 
  • #7
28
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i think the answer is Ns
 
  • #8
114
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It is indeed.
 

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