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P1112 Fall 2008
Homework #6
Due week of Oct 6.
Reading: 4.34.6,
Chapter 5.
Not all concepts will be covered in class – you are responsible
for all material in the reading and in the homework problems.
Problems:
1.
An athlete whose mass is 90.0 kg is performing
weightlifting exercises. Starting from the rest
position he lifts, with constant acceleration, a barbell
that weighs 490 N. He lifts the barbell a distance of
0.60 m in 1.6 s.
a) Draw a clearly labeled freebody diagram for the
barbell and for the athlete.
b) Use the diagrams in part a) and Newton’s laws to
find the total force that his feet exert on the ground as
he lifts the barbell.
2.
A box whose weight is w is pulled at constant
speed along a level floor by a force F that is directed
at an angle
θ
above horizontal.
The coefficient of
kinetic friction between the floor and box is μ
k
.
(a)
In terms of
θ
, μ
k
, and w, calculate the required
force F.
(b)
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 Fall '07
 LECLAIR,A
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