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Name_____________________________________________ House______________________ Class____
U3. L3. Newton’s 3rd Law & Normal & Tension Force
Directions: Answer the following questions.
1)
Identify the action-reaction pairs in the following situations:
a) A person stands on the ground
b)
A snowball hits someone in the back
c)
A baseball player catches a ball
d)
A gust of wind strikes a window
2)
A child causes a wagon to accelerate by pulling it with a horizontal force. Newton’s third law says that the wagon exerts an equal in
magnitude and opposite in direction force on the child. Why does the wagon accelerate? (Hint: draw a free-body diagram for each
object.)
3)
The Monster Book of Monsters (a 2 kg book) sits on top of a 10 kg table.
a. Draw the FBD and calculate the forces for the book.
Sketch
FBD
∑Fx = m * ax
∑Fy = m * ay
∑Fx = m * ax
∑Fy = m * ay
Object/system?
______________
b.
Draw the FBD and calculate the forces on the table.
Sketch
FBD
Object/system?
______________
OBJECTS IN MOTION STAY IN MOTION
Name_____________________________________________ House______________________ Class____
4)
A 300 kg bear sits in a 5 kg chair.
a. Draw the FBD and calculate the forces for the bear.
b.
5)
Draw the FBD and calculate the forces on the chair.
You and your friends build a treehouse with a pulley system. You (weight = 800 N) stand at the bottom and pull the rope taught so the
5kg bucket is accelerating at 0.5 m/s2.
a. Draw the FBD and calculate the forces on the bucket.
Sketch
FBD
∑Fx = m * ax
∑Fy = m * ay
∑Fx = m * ax
∑Fy = m * ay
Object/system?
______________
b.
Draw the FBD and calculate the forces on you!
Sketch
FBD
Object/system?
______________
OBJECTS IN MOTION STAY IN MOTION
Name_____________________________________________ House______________________ Class____
6)
A cat weighing 50N hangs at rest from a 15 kg chandelier.
a. Draw the FBD and calculate the forces on the cat.
b.
Draw the FBD and calculate the forces on the chandelier!
7)
A student pulls on a rope attached to a box of books and moves the box down the hall. The student pulls with a force of 185 N
horizontally. The box has a mass of 35.0 kg, and there is a force due to friction between the box and the floor that opposes motion by 25
N. Find the acceleration of the box.
8)
Explain why a rope climber must pull downward on the rope in order to move upward. Discuss the force exerted by the climber’s arms in
relation to the weight of the climber during the various stages of each “step” up the rope.
9)
A 2 kg box sits on a 3 kg box which sits on a 5 kg box. The 5 kg box rests on a table top. What is the normal force exerted on the 5 kg box
by the table top?
OBJECTS IN MOTION STAY IN MOTION