IGCSE/GCSE/O & A Level/IB/University Student Forum

Qualification => Subject Doubts => GCE AS & A2 Level => Math => Topic started by: nid404 on September 14, 2009, 04:34:16 pm

Title: Mechanics...need help guys!!
Post by: nid404 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....
Title: Re: Mechanics...need help guys!!
Post by: Saladin 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.
Title: Re: Mechanics...need help guys!!
Post by: nid404 on September 14, 2009, 05:15:46 pm: Quote from: The Dude 321 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.

no problem...I'll wait for astar..................as usual :P
Title: Re: Mechanics...need help guys!!
Post by: T.Q on September 14, 2009, 07:44:32 pm: Quote from: nid404 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....
is this M1 or what
Title: Re: Mechanics...need help guys!!
Post by: astarmathsandphysics 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.
Title: Re: Mechanics...need help guys!!
Post by: astarmathsandphysics on September 15, 2009, 10:04:27 am: Quote from: nid404 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....

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
Title: Re: Mechanics...need help guys!!
Post by: nid404 on September 15, 2009, 02:15:03 pm: Thank you very much