1.
What is the acceleration of the system
shown on the right if m
1
= 2 kg and m
2
= 4
kg?
Consider the forces on m
1
The weight of m
1
= m
1
g = 2 kg
×
9.8 ms
2
=
19.6 N acts vertically down on m
1
.
The tension T on the string pulls m
1
upward.
Assuming that m
1
moves up, the net force
on m
1
is T – 19.6.
If a is the acceleration of the system, then:
F
net
= m
1
a
T – 19.6 = 2a
….(i)
Consider the forces on m
2
The weight of m
2
= m
2
g = 4 kg
×
9.8 ms
2
= 39.2 N acts vertically
down on m
2
.
The tension T on the string pulls m
2
upward. Assuming that m
2
moves
down, the net force on m
2
is 39.2 – T .
Since a is the acceleration of the system:
F
net
= m
2
a
39.2 – T
= 4a
….(ii)
Adding equations (i) and (ii) gives:
39.2 – 19.6 = 6a
a = 3.27 ms
2
Using this value of a in equation (i) we have:
T – 19.6 = 2 (3.27)
T = 26.14 N
2.
The figure on the right, if
there is no friction between
the inclined plane and 3.0
kg mass, find the
acceleration of the masses
and the tension on the
string.
3 kg
40
o
5 kg
18.9 N
T
49 N
T
29.4 N
Consider the forces on the 3.0kg mass
The weight of the 3kg mass = 3
×
9.8 = 29.4 N acts vertically down.
The component of this down the plane = 29.4 sin 40
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 Fall '10
 George
 Physics, Acceleration, Force, Work, 10kg, 15 kg, 3.0kg, 15kg, 25.0g

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