Author Topic: Mechanics...need help guys!!  (Read 2069 times)

nid404

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Mechanics...need help guys!!
« on: September 14, 2009, 04:34:16 pm »
1) A balloon of total mass 840kg is rising vertically with constant speed.  As a result of realeasing some ballast, the balloon immediately accelerates at 0.5m/s2. Calculate the mass of the ballast released
2)A load of weight 7kN is being raised from rest with constant acceleration by a cable. After the load has been raised 20 m, the cable suddenly becomes slack. It continues to move up 4m before coming to instantaneous rest. Assuming no air resistance, find the tension in the cable before it became slack

THanx in advance....

Offline Saladin

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Re: Mechanics...need help guys!!
« Reply #1 on: September 14, 2009, 05:03:19 pm »
I think A star will be able to help you the best, becasue I have not yet started mechanics.

nid404

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Re: Mechanics...need help guys!!
« Reply #2 on: September 14, 2009, 05:15:46 pm »
I think A star will be able to help you the best, becasue I have not yet started mechanics.

no problem...I'll wait for astar..................as usual :P

Offline T.Q

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Re: Mechanics...need help guys!!
« Reply #3 on: September 14, 2009, 07:44:32 pm »
1) A balloon of total mass 840kg is rising vertically with constant speed.  As a result of realeasing some ballast, the balloon immediately accelerates at 0.5m/s2. Calculate the mass of the ballast released
2)A load of weight 7kN is being raised from rest with constant acceleration by a cable. After the load has been raised 20 m, the cable suddenly becomes slack. It continues to move up 4m before coming to instantaneous rest. Assuming no air resistance, find the tension in the cable before it became slack

THanx in advance....
is this M1 or what
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Offline astarmathsandphysics

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Re: Mechanics...need help guys!!
« Reply #4 on: September 14, 2009, 11:26:53 pm »
I only just say this. Am on a phone now. Will answer it when i get to a pc.

Offline astarmathsandphysics

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Re: Mechanics...need help guys!!
« Reply #5 on: September 15, 2009, 10:04:27 am »
1) A balloon of total mass 840kg is rising vertically with constant speed.  As a result of realeasing some ballast, the balloon immediately accelerates at 0.5m/s2. Calculate the mass of the ballast released
2)A load of weight 7kN is being raised from rest with constant acceleration by a cable. After the load has been raised 20 m, the cable suddenly becomes slack. It continues to move up 4m before coming to instantaneous rest. Assuming no air resistance, find the tension in the cable before it became slack

THanx in advance....

1)If the tension is T in the cable, using F=ma
Before ballast released
T-840g=0 so T=840g
After ballast of mass m released, the mass falls to 840-m
T-(840-m)g=.5(840-m)
840-840g+mg=420-0.5m
Make m the subject: mg+0.5m=840g -420so m(g+0.5)=-420+840g so m=(-420+840g)/(g+0.5)

2)First use suvat to find the acceleartion then F=ma to find the force
After the cable goes slack
s=4
u
v=0
a=-9.8
t
v^2=u^2+2as so 0=u^2+2*-9.8*4 so u^2=78.5 so u=sqrt(78.4)

Before the cable goes slack
s=20
u=0
v=sqrt(78.4)
a
t
v^2=u^2+2as so 78.4=0+2*a*20 so a=1.96m/s^2

Now use F=ma
T-mg=ma
T-7000=(7000/9.8)*1.96 so T=8400N

nid404

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Re: Mechanics...need help guys!!
« Reply #6 on: September 15, 2009, 02:15:03 pm »
Thank you very much