A 2 kg mass is attached to a string which is attached to a second?

Question

A 2 kg mass is attached to a string which is attached to a second mass 1 kg The string passes over a pulley and the two masses both hang down. They are released from rest. How long does it take for each to move 0.9 metres?
A. 0.52 s
B. 1.35 s
C. 0.74 s
D. 0.25 s
E. 0.17 s

Answer 1

Assuming no friction in the system and g=-10

First look at a FBD of the 2 kg mass
2*10-T=2*a
and the 1 kg mas
T-1*10=1*a

solve for a

T=a+10
20-a-10=2*a
a=10/3

y(t)=.5*10*t^2/3
y(t)=0.9=5*t^2/3
t=sqrt(0.9*3/5)
t=0.74
which is choice C

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Answer 2

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