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VCE Stuff => VCE Science => VCE Mathematics/Science/Technology => VCE Subjects + Help => VCE Physics => Topic started by: hard on September 04, 2008, 07:54:17 pm

Title: hards questions
Post by: hard on September 04, 2008, 07:54:17 pm: 1. what impulse is necessary to give a 4 kg mass a change in velocity of 2.5 ms-1?

2. a golf ball of mass 46 g is struck with such a force that ist acquires a velocity of 40 ms-1. Calculate the impulse necessary to produce the velocity. If the force is applied for 20 milliseconds what is the magnitude of the force applied?
Title: Re: hards questions
Post by: Flaming_Arrow on September 04, 2008, 08:08:36 pm: 1.

$I = mv$

$m = 4kg   v= 2.5 ms^{-1}$

$\implies I = 4 * 2.5$

$\boxed {I = 10 Ns}$

2.

$I = mv$

$m = 0.046kg   v= 40 ms^{-1}$

$\implies I = 0.046 * 40$

$\boxed {I = 1.84 Ns }$

$t = 0.020    m = 0.046$

$I = Ft$

$\implies F = \frac {I}{t}$

$\implies F   = \frac {1.84}{0.02}$

$\boxed {F = 92N}$
Title: Re: hards questions
Post by: hard on September 04, 2008, 09:10:19 pm: thnx man, easy q's but teacher didn't explain.
Title: Re: hards questions
Post by: hard on September 04, 2008, 09:10:39 pm: maybe that and i hate physics.
Title: Re: hards questions
Post by: cara.mel on September 04, 2008, 09:22:54 pm: Being picky:

impulse = change in momentum = p_f - p_i = m*v_f - m*v_i (or m* delta v)
(assuming m=constant, which it will be in VCE)
Title: Re: hards questions
Post by: hard on September 04, 2008, 09:29:12 pm: Quote from: caramel on September 04, 2008, 09:22:54 pm
Being picky:

impulse = change in momentum = p_f - p_i = m*v_f - m*v_i (or m* delta v)
(assuming m=constant, which it will be in VCE)

that's what it says in the book

can you show an example of how it can be used this way
Title: Re: hards questions
Post by: cara.mel on September 04, 2008, 09:37:29 pm: A 100g ball hits the ground at 20m/s, and bounces up at the same speed. Find the change in impulse on the ball

Initial v = 20m/s down = -20
Final v = 20m/s up = 20

I = m * (v_f-v_i) = .1(20 - -20) = .1*40 = 4Ns upwards

Edit: typo
Title: Re: hards questions
Post by: hard on September 04, 2008, 09:42:01 pm: thankyou