Download Chapter 4: Forces and the Laws of Motion Name Use Chapter 4 in

Chapter 4: Forces and the Laws of Motion
Name ________________________
Use Chapter 4 in your book pages 119 – 144 and your notes to answer the following questions.
Introduction to Forces
1) Forces cause objects to __________________________.
2) What is the difference between contact forces and field forces?
3) Why is force a vector quantity?
4) Draw a free body diagram for an apple hanging from a tree.
5) Draw a free body diagram and calculate the net force on a refrigerator that a person is sliding across the floor if
the person is pushing with a force of 32 N and force of friction opposing the motion is 12 N.
6) What is the affect of the forces on the refrigerator?
7) The object below is moving at a constant velocity to the right when the following forces are applied. What is the
net force acting on the object?
2 N left
5 N right
3 N left
8) What is the effect of the net force on the object in the above question?
9) The object below is moving at constant velocity to the right when the following forces are applied. What is the
net force acting on the object?
2 N left
6 N right
10) What is the effect of the net force on the object in the question above?
11) What is the net force on an object in equilibrium?
12) Fill in the table below
Symbol
Definition
The vector sum of all the forces acting on an object.
An applied force on an object like a push or pull.
The force due to gravity on an object.
The resistance to motion that occurs whenever 2 materials or media are in contact.
A tension force transmitted through a string or rope when it is pulled tight.
The normal force (or support force) exerted upward by a surface and is perpendicular to the surface.
Force Pairs
13) If two objects are in contact how do you compare the forces between the 2 objects?
14) Why don’t these forces cancel each other out?
15) Draw and label the force pairs on the picture below. The man is dropping a ball off the Leaning Tower of Pisa.
16) Why does the ball accelerate and the Earth does not accelerate?
17) Draw and label the 2 force pairs on the picture below. The weight is hanging from the ceiling on a rope.
Draw the free body diagram for the
weight.
If the rope is cut, why does the
weight accelerate?
18) To reach the finish line, a runner sprints from 5.2 m/s to 6.0 m/s in 2 seconds. Her mass is 50 kg. What is the
runner’s average acceleration?
19) What is the average backward force that the runner exerts on the ground?
20) What is average force that the ground exerts on the runner?
21) Why don’t these two forces cancel out?
Mass versus Weight
22) What is the difference between mass and weight?
23) What is the weight of a 300 kg mass on Earth?
24) The acceleration due to gravity on the moon is 1.6 m/s2. What is the weight of a 300 kg mass on the Moon?
25) The mass of a book is 54 g. What is the mass of this book on the Moon? Explain your answer.
26) You have a 20 N bar of gold on the Earth. You also have another 20 N bar of gold on the moon. Which bar of gold
has a greater mass? Why?
Net Force, Acceleration, and Mass
27) The acceleration of a sliding block is 2 m/s2. If the net force acting on a sliding block is tripled, what is the
acceleration of the block?
28) The acceleration of a sliding block is 1.8 m/s2. If the mass of the sliding block is tripled while a constant force is
applied, what is the acceleration of the block?
29) If the mass of a sliding block is tripled while the net force on it is tripled, how the does resulting acceleration
compare to the original acceleration?
30) Calculate the acceleration of a 40 kg crate of softball gear when pulled sideways with a net force of 200 N.
31) A 2.0 kg coconut falls on Gilligan’s Island. Ignoring air friction, what was the net force on the nut as it falls?
32) A snowball of mass 0.1 kg leaves little Joey’s hand at a speed of 15 m/s and comes to rest 0.15 seconds later.
Calculate the force on the snowball from Joey’ hand. (Calculate the acceleration first.)
33) A soccer ball kicked with a force of 13.5 N accelerates at 6.5 m/s2 to the right. What is the mass of the ball?
34) Look at the free body diagram below.
A book is pushed along a horizontal surface.
FN = ______
Fa = 30 N right
Ff = 5 N left
Fg = _______
m = 5 kg
35) Fnet = _____________________
36) a = ________________________
Force of Friction
37) List the four types of friction that we talked about in class from the type that opposes motion the most to the
type that opposed motion the least.
38) If you push horizontally with a force of 50 N on a crate and make it slide at constant velocity, what is the force of
friction that acts on the crate?
39) In the above case, if you increase your force, will the crate accelerate? Explain.
40) How does the force of static friction compare to the applied force on a huge box that you cannot move?
41) Explain what the coefficient of friction means?
42) A 95 kg clock at rest on a horizontal floor requires a 650 N force to set it in motion, After the clock is in motion, a
horizontal force of 560 N keeps it moving with a constant velocity, Find µs,mas and µk.
43) Look at the free body diagram below.
Fill in the blanks.
FN = __________
Fk = ________
Fa = __________
µk = 0.4
m = 8 kg
a = 0 m/s2
Fnet = __________________
What is the motion of the object? How do you know?
Fg = _______
Terminal Velocity
44) What is meant by free fall?
45) In free fall, why doesn’t a more massive object accelerate more than a less massive object?
46) What is the net force (magnitude and direction) that acts on a falling object with a weight of 10 N when it
encounters 4 N of air resistance? Draw the free body diagram.
47) What is the net force (magnitude and direction) that acts on a falling object with a weight of 10 N when it
encounters 10 N of air resistance?
48) Explain how the cross sectional area of an object and the speed of an object affect the force of air resistance on
an object if it is falling in air.
49) What is the acceleration of a falling object that has reached terminal velocity?
50) If you drop a pair of tennis balls simultaneously from the top of a building, they will strike the ground at the
same time. If you fill one of the balls with lead pellets and then drop then together, which one will hit the
ground first? Why? (Do not ignore air resistance)
51) A skydiver with a mass of 100 kg experiences air resistance of 700 N. What is the skydiver’s acceleration? (Find
the weight of the skydiver first.)
Centripetal Acceleration and Centripetal Force
52) Why is an object moving in a circle with constant tangential speed accelerating?
53) What is the direction of the acceleration?
54) A race car is moving along a circular track with a tangential speed of 30.0 m/s. The distance from the car to the
center of the track is 58.4 m. What is the centripetal acceleration of the car?
55) Why is the centripetal acceleration directed inward?
56) Explain what makes a passenger in a turning car slide toward the door of the car?
57) A Physics student twirls a set of keys with a mass of 0.5 kg in a circle at the end of a cord. If the keys have a
tangential speed of 7.0 m/s and the cord has a length of 0.34 m, what is the centripetal force on the keys?
58) A 40 kg child is riding the amusement park ride called the Rotor. After the ride gets up to the correct speed the
floor drops. If the centripetal force on the child is 533 N, determine the tangential speed of the child if the radius
of the ride is 2.90 meters.
Inertia
59) What is inertia?
60) In space which would be harder to move, a semi truck or Toyota Rav? Why?