Physics Test 3
What is the mass of a 954.6-kg elephant?
954.6 kg
What is the simple definition of a force?
A force is a push or pull
What is the more complex definition of a force?
A force is an action exerted on an object that may change the motion of an object.
What is the reaction to the gravity pulling down on a falling leaf?
The leaf pulls up on the Earth.
What are the parts of a free body diagram?
You draw the object and all of the forces acting on the object
When a model rocket is launched with a net force of 25.0 N, what acceleration will it experience if it has a mass of 35.0 g?
a = 𝐹𝑛𝑒𝑡/𝑚= (25.0𝑁) /(0.0350𝑘𝑔)= 714 𝑚/𝑠^2
What is the general term for the force exerted on you by the chair you are sitting on?
a normal force
When a 15,700 kg truck accelerates from rest to 15.0 m/s in 12.50 s, what net force acts on the truck?
a= (vf-vi)/delta t = (15.0 m/s - 0) / (12.50 s) = 1.20 m/s^2, Fnet =(15,700kg) (1.20 m/s^2) = 18,800 N
Calculate the acceleration due to gravity on the surface of Mars, given that its mass is 6.39 x 10^23 kg and its average radius is 3.389 x 10^6 m.
g=G (m/d^2) = ((6.673 x 10^-11)(Nm^2/kg^2)) (6.39x10^23kg)/(3.389X10^6m)^2)) = 3.71m/s^2
What do physicists call the resistance to any change in an object's motion?
inertia
Calculate the spring constant of a rubber band if it stretches 5.00 cm when a force of 3.55 N acts on it.
k = F/delta x = (3.55 N) / (0.0500 m) = 71.0 N/m
What is the mass of a 282,000-N rocket?
m = 𝑤/g= (282,000𝑁)/9.80𝑚/𝑠^2= 28,800 kg
What is the unit for force, and what is its relationship to the fundamental units?
1N = 1𝑘𝑔 (𝑚) /𝑠2
When walking your dog on a leash, what kind of force can you exert on him to keep him safe?
A tension force
Which of the following is NOT true about actions and reactions according to the Law of Interaction?
Actions and reactions act on the same system
What is an agent of a force?
An agent is the specific, immediate, and identifiable cause of a force.
Give an example of a field force.
Answers may vary but gravity, electricity, and magnetism are all field forces
Give an example of a contact force.
Answers may vary but typing on a keyboard involves contact forces
There are two kinds of forces. What are they?
Contact and Field
What is the branch of classical mechanics concerned with the study of forces and their effects on motion called?
Dynamics
Contact forces are an example of which kind of fundamental force?
Electromagnetic
A 49.5-kg child is playing on a Merry-Go-Round that has a diameter of 2.25 m. She is moving at a tangential speed of 5.32 𝑚𝑠ms. Calculate her centripetal force and her centripetal acceleration.
Fc = mv^2 / r = (49.5kg)(5.32 m/s) ^2 / (1.125 m) = 1250 N, ac = v^2/r = (5.32 m/s)^2 / (1.125 m) = 25.2 m/s^2
What is the gravitational force between two identical masses of 803 kg separated by 5.00 m?
Fg = G (m1m2)/d^2 = (6.673 x 10 ^-11)(Nm^2/kg^2) ((803kg)(803kg))/(5.00m)^2 = 1.72 x 10^-6 N
What is the equation associated with the Law of Acceleration?
Fnet
If a 2696-kg car decelerates at 2.315 𝑚𝑠2ms2, what net force acts on it?
Fnet = ma = (2696 kg) (-2.315 𝑚/𝑠^2) = -6241 N
Differentiate between the two types of forces.
For contact forces, the agent and receiver of the force must touch; for field forces, no contact is needed
Which one of the following statements is NOT part of the Law of Inertia?
For every action, there is an equal but opposite reaction
What do physicists call the resistance to motion or attempted motion?
Friction
Be able to draw a free body diagram of a baseball player sliding into second base.
Fx to the left, Normal force up, W down
The mass of the Earth is 5.97 x 1024 kg and its average distance from the Sun is 1.496 x 1011 m. If the gravitational force of attraction between the Sun and the Earth is 3.54 x 1022 N, what is the mass of the Sun?
G(m1m2/d^2), m1 = Fgd^2/Gm^2= ((3.54x10^22N)(1.496x10^11m)^2 / (6.673x10^-11 (Nm^2/kg^2)(5.97x10^24kg))= 1.99x10^30 kg
Which of the following is NOT true according to Newton's Universal Law of Gravitation?
Gravitational forces can be both attractive and repulsive
What are the four Fundamental Forces of Nature?
Gravitational, Electromagnetic, Strong Nuclear Force, Weak Nuclear Force
What is the property of an object that resists any change in its motion?
Inertia
Which of the following is NOT a description of acceleration according to Newton's Second Law of Motion? Acceleration _________.
Is directly proportional to the velocity of the system
A ski instructor pushes a 68.4-kg skier on waxed wooden skis on wet snow. How much acceleration does the skier experience if he pushes with a 155-N horizontal force?
N= W= mg= (68.4 kg) (9.80 m/s^2 ) = 670.32 N, Fk = mukN = (0.10)(670.32N) = 67.032 N, Fnet = Fnet - Fk = (155N) - (67.032N) = 87.968 N, a=Fnet/m = (87.968 N) / (68.4 kg) = 1.29 m/s^2
How much force is needed to start a 68.4-kg skier on waxed wooden skis on wet snow?
N=W = mg = (68.4kg)(9.80 m/s^2) = 670.32N, Fs, max = muN = (0.14)(670.32 N) = 93.8N
Be able to draw a free body diagram of a book resting on a table.
Normal force up and Weight down
What are the two types of surface friction?
Static (starting) and kinetic (sliding)
Which two fundamental forces act only on an atomic scale?
Strong Nuclear Force, Weak Nuclear Force
What is the other name of Newton's Second Law of Motion?
The Law of Acceleration
What is the other name of Newton's First Law of Motion?
The Law of Inertia
What is the other name of Newton's Third Law of Motion?
The Law of Interaction
What is the reaction to a person punching a desk?
The desk applies a force to the person's hand.
When a soccer player kicks a soccer ball, what is the agent of the force applied to the soccer ball?
The player's foot.
What is more elastic, the suspension springs in your car or a metal spoon?
The suspension springs in your car.
Which of the following is NOT true about an object in uniform circular motion?
The velocity is constant
Differentiate between weight and mass.
The weight of an object is a measure of the pull of gravity on that object, while the mass of an object is the measure of the amount of material in an object.
Be able to draw a free body diagram of a rocket during liftoff.
Thrust up, W down
What is the mathematical relationship between weight and mass?
W = mg
What is the weight of a 91.3-g ball?
W = mg = (0.0913 kg) (9.80 𝑚𝑠2ms2) = 0.895 N
