2.6 Analysing Impulse & Impulsive Force

7/25/2019 2.6 Analysing Impulse & Impulsive Force

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2.6 Analying impulse and2.6 Analying impulse and

impulsive forceimpulsive force


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Learning Outcome :Learning Outcome : Explain what an impulsive force is.Explain what an impulsive force is.

Give examples of situation involvingGive examples of situation involvingimpulsive forces.impulsive forces.

efine impulse as a change of momentum!efine impulse as a change of momentum!

i.ei.e "t # mv $ mu"t # mv $ mu

efine impulsive force as the rate of changeefine impulsive force as the rate of changeof momentum in collision or explosion i.eof momentum in collision or explosion i.e

" # mv $ mu" # mv $ mu

tt


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Learning Outcome :Learning Outcome :

Explain the effect of increasing orExplain the effect of increasing or

decreasing time of impact on magnitude ofdecreasing time of impact on magnitude of

the impulsive forces.the impulsive forces.

escri%e situation where an impulsiveescri%e situation where an impulsive

force needs to %e reduced and suggestforce needs to %e reduced and suggest

ways to reduce it.ways to reduce it.

escri%e situation where an impulsiveescri%e situation where an impulsive

force is %eneficialforce is %eneficial


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"ormula of &mpulse"ormula of &mpulse

&mpulse is the product of force and time&mpulse is the product of force and time &mpulse experience %y the %all&mpulse experience %y the %all

&mpulse # "t&mpulse # "t

&mpulse # momentum change&mpulse # momentum change

# mv $ mu# mv $ mu

'nit : (gms)* or +s'nit : (gms)* or +s


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600kg600kgA car of mass is movingA car of mass is moving

with velocity of . A netwith velocity of . A net

force of is applied on theforce of is applied on thecar for . "ind the impulsecar for . "ind the impulse

exerted on the car and henceexerted on the car and hencedetermine the final velocity ofdetermine the final velocity of

the car.the car.

15s15s

200N200N

30m/s30m/s

Example * :Example * :


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Answer:

&mpulse # " t# ,2-- ,*/

# 0---+s

&mpulse # mv ) mu ,0--- # 6--v ) 6--,0-

6--v # 0--- 1 *---

v # 2*---36--# 0/ m3s


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4hat is impulsive force54hat is impulsive force5

&mpulsive force is defined as the&mpulsive force is defined as the

rate of change of momentum in arate of change of momentum in a

reaction.reaction.

&t is a force which acts on an&t is a force which acts on an

o%ect for a very short intervalo%ect for a very short interval

during a collision or explosion.during a collision or explosion.


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An &mpulsive "orce is 7eneficialAn &mpulsive "orce is 7eneficial


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Example 2:Example 2:

A car of mass *---8g istraveling with a

velocity of 2/ m3s. 9he car

hits a street lamp and is

stopped in -.-/ seconds.

4hat is the impulsive forceacting on the car during

the crash5


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Answer :Answer :

&mpulsive "orce :&mpulsive "orce :

" # m,v)u" # m,v)u

tt

# *---, - $ 2/ # *---, - $ 2/

-.-/-.-/ # ) /--!---+# ) /--!---+


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Effect of time on impulsive forceEffect of time on impulsive force

* : Long ump* : Long ump 9he long ump pit is filled9he long ump pit is filled

with sand to increase thewith sand to increase the

reaction time whenreaction time when

athlete land on it.athlete land on it. 9his is to reduce the9his is to reduce the

impulsive force acts onimpulsive force acts on

the leg of the athletethe leg of the athlete

%ecause impulsive force%ecause impulsive forceis inversely proportionalis inversely proportional

to the reaction time.to the reaction time.


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Effect of 9ime on &mpulsiveEffect of 9ime on &mpulsive

"orce 2 : ;igh ump"orce 2 : ;igh ump uring a high ump! auring a high ump! a

high umper will land onhigh umper will land on

a thic8! soft mattressa thic8! soft mattress

after the ump.after the ump. 9his is to increase the9his is to increase the

reaction time andreaction time and

hence reduces thehence reduces the

impulsive force actingimpulsive force acting

on the high umper.on the high umper.

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2.6 Analysing Impulse & Impulsive Force