Physics Workbook 5c:
The Saga of Sally & Hank
Vectors
1.
A dog trots 30 m from home east, then turns and trots 50m 37¡ north of
east. Draw his total displacement.
2.
A cow ambles west for 400 m, then turns and wanders in a straight line
in another direction. Her total
displacement turns out to be 600m in a direction 53¡ north of west. Draw the second leg of the journey.
The Saga Begins: Part I
1.
A 50 N bag hangs from a rope attached to a limb.
Draw a FBD of the bag.
Is the bag in equilibrium?
Sum the forces acting on the bag.
What is this sum equal to?
Find the tension in the rope.
2.
A squirrel appears and gnaws the rope in two to allow his buddies on the
ground to catch the bag of goodies.
Draw a FBD of the bag.
Is the bag in equilibrium?
Sum the forces acting on the bag.
What is this sum equal to?
Find the tension in the rope.
3.
Suddenly an orangutan appears and in a daring act swings down from the
limb and grabs the rope. Then she begins pulling the rope upward at a
constant speed of 8 m/s.
Draw a FBD of the bag.
Is the bag in equilibrium?
Sum the forces acting on the bag.
What is this sum equal to?
Find the tension in the rope.
4.
When she sees a bear approaching the tree eying the bag, she begins to
pull faster, causing the bag to speed up with an acceleration of 4 m/s2.
Draw a FBD of the bag.
Is the bag in equilibrium?
Sum the forces acting on the bag.
What is this sum equal to?
Find the tension in the rope.
5. But, not fast enough. The 80 kg bear leaps up and grabs the bag and rides it down,
causing it to slip in the orangutan's grasp, and fall at a constant speed of 3
m/s.
Draw a FBD of the bag.
Is the bag in equilibrium?
Sum the forces acting on the bag.
What is this sum equal to?
Find the tension in the rope.
6.
Then, the stubborn orangutan exerts all her strength and manages to slow
the fall at a rate of 1 m/s2.
Draw a FBD of the bag.
Is the bag in equilibrium?
Sum the forces acting on the bag.
What is this sum equal to?
Find the tension in the rope.
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of First Day
7.
But alas, the extra weight proves too much for the branch, which breaks,
plunging bear, bag, orangutan and limb to the ground. The bear leaps up and bounds away, dragging the bag behind
him, applying a force of 60N to the rope, causing it to follow him reluctantly
at a constant speed of 7 m/s. (The
impact causes the orangutan to lose her grip.)
Draw a FBD of the bag.
Is the bag in equilibrium?
Sum the forces acting on the bag.
What is this sum equal to?
Find the net friction force on the bag .
8.
The dazed, but unharmed, orangutan finally recovers her composure, and
leaps to her feet. Unlike
the bear, she is unhampered by the bag, she quickly catches up and dives onto
the bag. The added 30 kg mass of
the orangutan increases the friction force which slows the bear, (still
applying a 60N force to the rope) down at a rate of 2 m/s2. (don't forget the bear has a mass of 80 kg and the bag of
goodies has a mass of 5 kg.)
Draw a FBD of the bag.
Is the bag in equilibrium?
Sum the forces acting on the bag-orangutan
mass.
What is this sum equal to?
Find the net friction force acting on the
bag-orangutan mass.
9.
But then the bag hits a rock, causing the orangutan to fall off, and the
bag and bear, who now pulls even harder trying to escape the orangutan with a
80 N force, to move off speeding up as it goes.
Draw a FBD of the bag.
Is the bag in equilibrium?
Sum the forces acting on the bag.
What is this sum equal to?
Find the acceleration of the bag.
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10.
A 200 N block sits on a horizontal surface and a dog tugs the rope
attached to it with a force of 80 N, but fails to budge it.
Draw a FBD of the block.
Is the block in equilibrium?
Sum the forces acting on the bag.
What is this sum equal to?
Find the static friction force.
11.
The 200 N block finally begins to move when the dog jerks on the rope
with a mighty lunge and he finds that he can now make it move at a constant
speed of 2 m/s with a force of only 50 N.
Draw a FBD of the block.
Is the block in equilibrium?
Sum the forces acting on the bag..
What is this sum equal to?
Find the kinetic friction force.
13.
Now the dog increases the force back to 60N and the block begins to
accelerate .
Draw a FBD of the block.
Is the block in equilibrium?
Sum the forces acting on the bag.
What is this sum equal to?
What must be this acceleration?
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