forces and angles physics 11. more bad jokes… review: free-body diagrams: free-body diagrams are...
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Forces and AnglesPhysics 11
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More bad jokes…
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Review: Free-body diagrams:
Free-body diagrams are used to show the relative magnitude and direction of all forces acting on an object. What if some of the
forces were not in the x or y plane???????
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Forces at angles:
We will break the forces with angles into their x and y components using trigonometry!
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Review: Fnet
Remember we are only worried about Fnet in the direction of the motion So sometimes we really only need either
the x or y component of the force at an angle.
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Example 1:
You need to move a 25.5 kg wooden crate across a wooden floor (µ=0.20). You pull with a rope attached at a 15º to the horizontal with a force of 276N.
a. Calculate the Fapp(X) and Fapp(Y).
b. What is the acceleration of the crate?
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a.
Fapp(x)= 276 N * cos 15
= (276)(0.9659) = 267 N
Fapp(y)= 276 N * sin 15
= (276)(0.2588) = 71.4 N
=15º
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b. FBD Only need to consider x axis forces as that is the plane of
the motion. Ff = µFN
= (0.20)[(25.5)(9.81) = 50.0 N Fnet= Fapp(x) + Ff
= 267N – 50N = 217 N
Fnet= ma217= (25.5)a
8.5 m/s2 = a
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Is it easier to push or pull a sled?
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Pulling a Sled
A child of 35kg is sitting on a sled that has a coefficient of kinetic friction of 0.10 with the snow. If the parent who is pulling the sled pulls up with an angle of 25°, with what are the component forces? Draw FBD
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FBD
Fg
Ff
FN
Fa
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Break Applied Force into Components
Fay
Fax
Fa
aay
aay
aay
aax
aax
aax
FF
FF
FF
FF
FF
FF
)423(.
)25sin(
sin
)906(.
)25cos(
cos
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Example: Pushing a Sled
A child of 35kg is on a sled that has a µk =0.10 with the snow. If the parent who is pushing the sled pushes down with an angle of 25°, with what are the component forces. Draw FBD.
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FBD
Fg
Ff
FN
Fa
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Break Applied Force into Components
Fay
Fax
Fa
aay
aay
aay
aax
aax
aax
FF
FF
FF
FF
FF
FF
)423.(
)25sin(
sin
)906(.
)25cos(
cos
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Practice:
Force Components: Vectors WS Do 5d and 6c together
Page 171 #11, 12 (assume no Ff) Page 208 # 24, 25