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THIS THREAD WAS INCORRECTLY PLACED IN THE CLASSICAL PHYSICS FORUM, SO THERE IS NO TEMPLATE
Hi, everyone.
my teacher stuck me with these questions and i am need of a little help answering question 2.
here's my answers to question 1 first.
1a) a=0, as system would be in equilibrium when F=0
b) F=5mgN, as for a=5m/s the acceleration of B has to equal 2.5m/s and as its in equilibrium F has just got to equal m*a which is 2.5*2mg=5mgN
c) F=mga
i think my answers are right but if im making a simple mistake let me know.
now my attempts at 2.
2a) first, B has to x/2 above the ground for the full system to work so original potential energy is 2mgx/2=mgx assuming A starts on the ground. now its the following kenetic energy bits that are confusing me because there will be two different V's one for A and one for B. V_{A} = 2V_{B} so assuming no energy gets lost to heat via friction whatever all of the gravitational energy plus energy input from F has to turn into kinetic energy so im thinking.
mgx + Fx = 1/2mV_{A} ^{2} + mV_{B} ^{2}
which kind of works if your given enough information. but part B doesn't i don't think.
2b) substituting values into my answer to 2a
98 + 196 = 1/2[ V_{A} ^{2} + 2V_{B} ^{2} ]
so V_{A} ^{2} + 2V_{B} ^{2} = 588N
and V_{A} = 2V_{B}
so with further manipulation i get V_{A} = 19.8m/s
but using logic from question 1. if F=19.6 and B has a mass of 2kg, the acceleration of B = 9.8m/s ^{2} therefore acceleration of A = 19.6m/s ^{2} and then using SUVAT.
s=10m u=0 v=? a=19.6 m/s ^{2}
v ^{2} = u ^{2} +2as
v = 23.2m/s
which is different. iv tried multiple times and i can't figure out what im doing wrong. im pretty sure its the WEP part not the SUVAT part as im better at that but i do not know.
please help.
Hi, everyone.
my teacher stuck me with these questions and i am need of a little help answering question 2.
here's my answers to question 1 first.
1a) a=0, as system would be in equilibrium when F=0
b) F=5mgN, as for a=5m/s the acceleration of B has to equal 2.5m/s and as its in equilibrium F has just got to equal m*a which is 2.5*2mg=5mgN
c) F=mga
i think my answers are right but if im making a simple mistake let me know.
now my attempts at 2.
2a) first, B has to x/2 above the ground for the full system to work so original potential energy is 2mgx/2=mgx assuming A starts on the ground. now its the following kenetic energy bits that are confusing me because there will be two different V's one for A and one for B. V_{A} = 2V_{B} so assuming no energy gets lost to heat via friction whatever all of the gravitational energy plus energy input from F has to turn into kinetic energy so im thinking.
mgx + Fx = 1/2mV_{A} ^{2} + mV_{B} ^{2}
which kind of works if your given enough information. but part B doesn't i don't think.
2b) substituting values into my answer to 2a
98 + 196 = 1/2[ V_{A} ^{2} + 2V_{B} ^{2} ]
so V_{A} ^{2} + 2V_{B} ^{2} = 588N
and V_{A} = 2V_{B}
so with further manipulation i get V_{A} = 19.8m/s
but using logic from question 1. if F=19.6 and B has a mass of 2kg, the acceleration of B = 9.8m/s ^{2} therefore acceleration of A = 19.6m/s ^{2} and then using SUVAT.
s=10m u=0 v=? a=19.6 m/s ^{2}
v ^{2} = u ^{2} +2as
v = 23.2m/s
which is different. iv tried multiple times and i can't figure out what im doing wrong. im pretty sure its the WEP part not the SUVAT part as im better at that but i do not know.
please help.
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