MiniDrill 1 Due Today

1
Mini-Drill (1) Due Today

• Problem 24, page 108 A shopper in a supermarket
  pushes a loaded cart with a horizontal force of
  10 N. The cart has mass of 30 kg. (b) How far
  will it move in 3.0 s if the shopper places her
  30 N baby in the cart before she begins to push
  it?

2
Step 1.) Sketch
y
x
3
Step 2.) Acceleration
4
Step 3.) Motion Equations
Horizontal
Vertical
5
Step 4.) Algebraic Solution
6
Mini-Drill (2) Due Today
Prove q1 q2.
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Mini-Drill (3) Due Today

• Assume that mk 0.2 in the previous problem.
  What is the acceleration? Why did you not need to
  know the mass of the block?

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Step 1) Sketch
y
m
x
9
Step 2.) Acceleration
where
10
Step 2.) Acceleration
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Exam Example (1)

• A box weighing 225 N is pulled across the floor
  with a force of 350 N exerted upward at an angle
  33.3o above the horizontal. If mk 0.47, how
  long does it take to move the box 2.00 m starting
  from rest?

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Step 1.) Sketch
y
x
(1)
(2)
13
Step 2.) Acceleration
(1)
(2)
(3)
Mini-Drill (1) Due Today Show
14
Step 2.) Acceleration
Solution to Mini-Drill (4) find ax (Note there
is an easier way to solve for the acceleration
than the following steps see mini-drill (3)
acceleration solution).
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Step 2.) Acceleration
Seems large?
16
Step 3.) Motion Equations
Horizontal
Vertical
17
Step 4.) Algebraic Solution
Solution to Mini-Drill (5)
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Mini-Drill (6) Due Today

• A box weighing 225 N is pulled across the floor
  with a force of 350 N exerted downward at an
  angle 33.3o below the horizontal. If mk 0.47,
  how long does it take to move the box 2.00 m
  starting from rest?

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Step 1.) Sketch
y
x
(1)
(2)
20
Step 2.) Acceleration
(1)
(2)
(3)
Quicker less algebra method
From eq(2) Find n the normal force.
Then find a numerical value for fk using eq (3),
then find ax from Eq (1)
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Step 2.) Acceleration
(2)
(3)
(1)
To find mass
22
Step 3.) Motion Equations
Horizontal
Vertical
23
Step 4.) Algebraic Solution
Solution to Mini-Drill (3)
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Mini-Activity (2) Solution

• You press your physics textbook flat against a
  vertical wall with your hand. What is the
  direction of the friction force exerted by the
  wall on the book? Draw the Free-body diagram.

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Mini-Activity Solution
Direction of static friction force is upward.
wall
book
y
x