Physics test II

In Case A an object is moving straight downward with a constant speed of 9.80 m/s, while in Case B an object is moving straight downward with a constant acceleration of magnitude 9.80 m/s2. Which one of the following is true? (a) A nonzero net external force acts on the object in both cases. (b) A nonzero net external force acts on the object in neither case. (c) A nonzero net external force acts on the object in Case A only. (d) A nonzero net external force acts on the object in Case B only.

(d) A nonzero net external force acts on the object in Case B only.

What's Newtons 1ST Law of Motion?

-An object continues in a state of rest or in a state of motion at a constant speed along a straight line, unless compelled to change that state by a net force. -indicates that a state of rest (zero velocity) and a state of constant velocity are completely equivalent, in the sense that neither one requires the application of a net force to sustain it. -sometimes called the law of inertia -in the absence of a net force you should move with a constant velocity

What is Newton's 3RD Law of motion?

-also called the Action - reaction law -Whenever one body exerts a force on a second body, the second body exerts an oppositely directed force of equal magnitude on the first body -3 keys: Equal magnitude forces Opposite directions Apply on different objects -Whenever one object exerts a force on a second object, the second object exerts an oppositely directed force of equal magnitude on the first object. -For every action (force) there is an equal, but opposite, reaction.

What's net force?

3 forces act simultaneously on a body, and the net force is the vector sum of all of them. EF

A box has a weight of 150 N and is being pulled across a horizontal floor by a force that has a magnitude of 110 N. The pulling force can point horizontally, or it can point above the horizontal at an angle theta. When the pulling force points horizontally, the kinetic frictional force acting on the box is twice as large as when the pulling force points at the angle theta. Find theta.

43 degrees

What's Newton's 2ND Law of motion?

A net external force EF causes the object to accelerate, When a net external force acts on an object of mass m, the acceleration that results is directly proportional to the net force and has a magnitude that is inversely proportional to the mass. The direction of the acceleration is the same as the direction of the net force. SI Unit of Force: kgm/s (N) 2 newton states that the acceleration is the net force divided by the mass The acceleration is directly proportional to EF, and inversely proportional to the mass. a and EF - same direction

What is force?

A push or a pull

what is the centripal acceleration equation?

Ac= v^2/r.

What are The Accelerations Produced by Action and Reaction Forces

Although the action and reaction forces have the same magnitude, they do not create accelerations of the same magnitude, because the spacecraft and the astronaut have different masses. According to Newton's second law, the astronaut, having a much smaller mass, will experience a much larger acceleration. In applying the second law, we note that the net force acting on the spacecraft is EF=P while the net force acting on the astronaut is EF= -P

What is the Definition of an Inertial Reference Frame

An inertial reference frame is one in which Newton's law of inertia is valid. The acceleration of an inertial reference frame is zero, so it moves with a constant velocity. All of Newton's laws of motion are valid in inertial reference frames, and when we apply these laws, we will be assuming such a reference frame. In particular, the earth itself is a good approximation of an inertial reference frame.

What's the equation for The Accelerations Produced by Action and Reaction Forces?

As= P/Ms

What is Fxmax and it's equation

At the instant of the block begins to slide. and fsmax= Us FN

Which of the following statements about centripetal acceleration is true? (a) An object moving at a constant velocity cannot have a centripetal acceleration. (b) An object moving at a constant speed may have a centripetal acceleration.

Both

What's the equation for Newtons 2ND Law?

EF = ma or a = EF/m

What is the equation for Newton's Second Law (Horizontal Direction)

EFx = MAx =0

What are the equations for the vector nature of Newton's second law of motion (Two - dimension)?

EFx = max EFy = may

What's the equation for Weight and true weight discrepancies using Newton's second law in the VERTICAL direction?

EFy= +Fn-mg+ma -a is the acceleration of the elevator and person -g is the magnitude of the acceleration due to gravity and can never be a negative quantity - However, the acceleration a may be either positive or negative, depending on whether the elevator is accelerating upward () or downward ()

What is NEWTON'S LAW OF UNIVERSAL GRAVITATION?

Every object in the universe exerts an attractive force on every other.Every particle in the universe exerts an attractive force on every other particle. A particle is a piece of matter, small enough in size to be regarded as a mathematical point. For two particles that have masses m1 and m2 and are separated by a distance r, the force that each exerts on the other is directed along the line joining the particles (see Figure 4.9) and has a magnitude given by F=G*m1m2/r2

gravitational force formula?

F = G [(m1 x m2)/r^2] where G is universal constant.

What's the equation for NEWTON'S LAW OF UNIVERSAL GRAVITATION

F = G*m1×m2/r2 G: universal gravitational constant G = 6.673 x 10-11 N.m2/kg2 -When applying Newton's gravitation law to uniform spheres of matter, remember that the distance r is between the centers of the spheres, not between the surfaces.-

What's the equation for force?

F=MA

What's Normal Force (Fn)

FN: a surface exerts a force on an object with which it is in contact, is perpendicular to the surface Normal force and Weight - NEWTON'S 3rd LAW it's equal to weight

How do you solve for Fn?

FN= mg +ma

How do you find the tension of centripital force?

Fc= T= mv^2/r (newtons)

What is the centripital FORCE equation?

Fc= mv^2/r m= object of mass It's The net force causing the centripetal acceleration

What is static frictional force

Fs before slide Direction: opposite to F (applied force). Magnitude: fs = F.

What equation can be used to determine the acceleration components from the given forces in a vector nature?

Newton's second law equations a= (magnitude)cos/sin/tan(angle)= N Example: (15 N)cos 67° 6 N

A freight train is accelerating on a level track. Other things being equal, would the tension in the coupling between the engine and the first car change if some of the cargo in the last car were transferred to any one of the other cars?

No, because the transfer described does not change the total mass being pulled by the engine.

Newton's second law indicates that when a net force acts on an object, it must accelerate. Does this mean that when two or more forces are applied to an object simultaneously, it must accelerate?

No, because two or more forces can cancel each other, leading to a net force of zero.

What's the equation for EF at an angle?

Perpendicular, F2 = FX2 + FY2

What's the equation for SI Unit of Force aka a Newton?

SI Unit of F= (kg)(m/s^2)=kg*m/s^2

What determines the magnitude of force?

The magnitude of the force: depends on masses of two objects distance between them (r)

What's the purpose of a net force acting on an object?

The purpose served when a net force acts on an object is not to sustain the object's velocity, but, rather, to change it.

What is W (weight?) and it's equation

The weight of an object on or above the earth is the gravitational force that the earth exerts on the object. The weight always acts downward, toward the center of the earth. On or above another astronomical body, the weight is the gravitational force exerted on the object by that body. -SI Unit of Weight: newton (N) -W=mg

What are the types of forces and what law applies to all of them?

Types of Forces: Gravitational force (Section 4.7) Normal force (Section 4.8) Frictional forces (Section 4.9) Tension force (Section 4.10). and Newton's 2ND Law

How do you find displacement?

Using equations x= v,0x*t +1/2*ax*t^2 and y= v,0y*t + 1/2* ay*t^2 v0x= velocitiy intial ex: (0 m/s)(65 s)+1/2 (0.011 m/s^2)(65 s)^2

What equation do you use if more than two forces

Using ∑F = 0

what's the work done on an object by a constant force formula

W = (F cos theta)s

weight formula?

W = G [(mass of earth x mass of object)/r^2]

What's the equation for the magnitude of the weight?

W= G Me*m/r^2 "m"= mass of object "Me"= mass of the earth

What equation would you use if you know Me, object of mass and R?

W=G*MEm/rE2 G*ME/rE2=9.8

What are frictional forces?

When the object moves or attempts to move along the surface, a force occurs that is parallel to the surface.

Object A weighs twice as much as object B at the same spot on the earth. Would the same be true at a given spot on Mars?

Yes, because the ratio of the two weights depends only on the masses of the objects, which are the same on the earth and on Mars.

The speedometer of your car shows that you are traveling at a constant speed of 35 m/s. Is it possible that your car is accelerating?

Yes, if you are going around a curve.

What's the centripetal acceleration formula

a = v^2/r *The centripetal acceleration vector always points toward the center of the circle and continually changes direction as the object moves.

A 10-kg suitcase is placed on a scale that is in an elevator. In which direction is the elevator accelerating when the scale reads 75 N and when it reads 120 N? (a) Downward when it reads 75 N and upward when it reads 120 N (b) Upward when it reads 75 N and downward when it reads 120 N (c) Downward in both cases (d) Upward in both cases

a) Downward when it reads 75 N and upward when it reads 120 N

Three particles have identical masses. Each particle experiences only the gravitational forces due to the other two particles. How should the particles be arranged so each one experiences a net gravitational force that has the same magnitude? (a) On the corners of an equilateral triangle (b) On three of the four corners of a square (c) On the corners of a right triangle

a) On the corners of an equilateral triangle

In which one of the following situations could an object possibly be in equilibrium? (a) Three forces act on the object; the forces all point along the same line but may have different directions. (b) Two perpendicular forces act on the object. (c) A single force acts on the object. (d) In none of the situations described in (a), (b), and (c) could the object possibly be in equilibrium.

a) Three forces act on the object; the forces all point along the same line but may have different directions.

A rope is used in a tug-of-war between two teams of five people each. Both teams are equally strong, so neither team wins. An identical rope is tied to a tree, and the same ten people pull just as hard on the loose end as they did in the contest. In both cases, the peo- ple pull steadily with no jerking. Which rope sustains the greater tension? (a) the rope tied to the tree (b) the rope in the tug-of-war (c) do the ropes sustain the same tension?

a) the rope tied to the tree

What is the acceleration equation?

a= change in velocity/change in time

A box rests on the floor of an elevator. Because of static friction, a force is required to start the box sliding across the floor when the elevator is (a) stationary (b) accelerating upward (c) accelerating downward. Rank the forces required in these three situations in ascending order—that is, smallest first.

accelerating downward, stationary, accelerating upward

A stone is thrown from the top of a cliff. Air resistance is negligible. As the stone falls, is it (a) in equilibrium (b) not in equilibrium?

b) (b) not in equilibrium?

When a body is moved from sea level to the top of a mountain, what changes? (a) the body's mass (b) its weight (c) both its mass and its weight

b) its weight

What is adjacent?

"Adjacent" is adjacent (next to) to the angle

What is hypotenuse?

"Hypotenuse" is the long one

What is opposite?

"Opposite" is opposite to the angle θ

A car is traveling in uniform circular motion on a section of road whose radius is r (see the drawing). The road is slippery, and the car is just on the verge of sliding. (a) If the car's speed were doubled, what would have to be the smallest radius in order that the car does not slide? Express your answer in terms of r. (b) What would be your answer to part (a) if the car were replaced by one that weighed twice as much, the car's speed still being doubled?

(a) 4r (b) 4r

All of the following, except one, cause the acceleration of an object to double. Which one is the exception? (a) All forces acting on the object double. (b) The net force acting on the object doubles. (c) Both the net force acting on the object and the mass of the object double. (d) The net force acting on the object remains the same, while the mass of the object is reduced by a factor of two

(a) All forces acting on the object double.

A father and his seven-year-old daughter are facing each other on ice skates. With their hands, they push off against one another. Which one or more of the following statements is (are) true? (a) Each experiences an acceleration that has a different magnitude. (b) Each experiences an acceleration of the same magnitude. (c) Each experiences a pushing force that has a different magnitude. (d) Each experiences a pushing force that has the same magnitude.

(a) Each experiences an acceleration that has a different magnitude.

The car in the drawing is moving clockwise around a circular section of road at a constant speed. What are the directions of its velocity and acceleration at (a) position 1 (b) position 2 Specify your responses as north, east, south, or west.

(a) The velocity is due south and the acceleration is due west. (b) The velocity is due west and the acceleration is due north.

Would a change in the earth's mass affect (a) the banking of airplanes as they turn (b) the banking of roadbeds (c) the speeds with which satellites are put into circular orbits (d) the performance of the loop-the-loop motorcycle stunt

(a) Yes. (b) Yes. (c) Yes. (d) Yes.

The acceleration due to gravity on the moon is one-sixth that on earth. (a) is the true weight of a person on the moon less than, greater than, or equal to the true weight of the same person on earth? (b) Is the apparent weight of a person in orbit about the moon less than, greater than, or equal to the apparent weight of the same person in orbit about the earth?

(a) less than (b) equal to

Which of the following statements can be explained by Newton's first law? (A); When your car suddenly comes to a halt, you lunge forward. (B); When your car rapidly accelerates, you are pressed backward against the seat. (a) Neither A nor B (b) Both A and B (c) A but not B (d) B but not A

(b) Both A and B

The net external force acting on an object is zero. Which one of the following statements is true? a) The object can only be stationary. (b) The object can only be traveling with a constant velocity. (c) The object can be either stationary or traveling with a constant velocity. (d) The object can only be traveling with a velocity that is changing.

(c) The object can be either stationary or traveling with a constant velocity

All of the following, except one, cause the acceleration of an object to double. Which one is the exception? (a) All forces acting on the object double. (b) The net force acting on the object doubles. (c) Both the net force acting on the object and the mass of the object double. (d) The net force acting on the object remains the same, while the mass of the object is reduced by a factor of two.

c) Both the net force acting on the object and the mass of the object double.

Suppose that the coefficients of static and kinetic friction have values such that µs = 1.4µk for a crate in contact with a cement floor. Which one of the following statements is true? (a) The magnitude of the static frictional force is always 1.4 times the magnitude of the kinetic frictional force. (b) The magnitude of the kinetic frictional force is always 1.4 times the magnitude of the static frictional force. (c) The magnitude of the maximum static frictional force is 1.4 times the magnitude of the kinetic frictional force.

c) The magnitude of the maximum static frictional force is 1.4 times the magnitude of the kinetic frictional force.

The net external force acting on an object is zero. Which one of the following statements is true? (a) The object can only be stationary. (b) The object can only be traveling with a constant velocity. (c) The object can be either stationary or traveling with a constant velocity. (d) The object can only be traveling with a velocity that is changing.

c) The object can be either stationary or traveling with a constant velocity.

A circus performer hangs stationary from a rope. She then begins to climb upward by pulling herself up, hand over hand. When she starts climbing, is the tension in the rope (a) less than (b) equal to (c) greater than it is when she hangs stationary?

c) greater than it is when she hangs stationary?

Two cars are identical, except for the type of tread design on their tires. The cars are driven at the same speed and enter the same unbanked horizontal turn. Car A cannot negotiate the turn, but car B can. Which tread design, the one on car A or the one on car B, yields a larger coefficient of static friction between the tires and the road?

car B

What are noncontact forces or action-at-a-distance forces

circumstances, however, in which two objects exert forces on one another even though they are not touching

How do you determine cosine

cos(θ) = Adjacent / Hypotenuse

During the final stages of descent, a sky diver with an open parachute approaches the ground with a constant velocity. There is no wind to blow him from side to side. Which one of the following statements is true? (a) The sky diver is not in equilibrium. (b) The force of gravity is the only force acting on the sky diver, so that he is in equilibrium. (c) The sky diver is in equilibrium because no forces are acting on him. (d) The sky diver is in equilibrium because two forces act on him, the downward-acting force of gravity and the upward-acting force of the parachute.

d) The sky diver is in equilibrium because two forces act on him, the downward-acting force of gravity and the upward-acting force of the parachute.

A penny is placed on a rotating turntable. Where on the turntable does the penny require the largest centripetal force to remain in place, at the center of the turntable or at the edge of the turntable?

edge of the turntable

What are internal forces?

forces that one part of an object exerts on another part of the object and are not included in Equation for Newton's law

How to determine Us

fsmax= Us FN since fsmax = F F = Us FN 1. Us = F/FN 2. TAN of incline angle

What are non-contact forces?

gravity and magnets

An object is in equilibrium when __________

it has zero acceleration

Two satellites are placed in orbit, one about Mars and the other about Jupiter, such that the orbital speeds are the same. Mars has the smaller mass. Is the radius of the satellite in or- bit about Mars less than, greater than, or equal to the radius of the satellite orbiting Jupiter?

less than

What's the mass?

measure inertia. In KG

A stack of books whose true weight is 165 N is placed on a scale in an elevator. The scale reads 165 N. From this information alone, can you tell whether the elevator is moving with a constant velocity of 2 m/s upward, is moving with a constant velocity of 2 m/s downward, or is at rest?

no

Other things being equal, would it be easier to drive at high speed around an unbanked horizontal curve on the moon than to drive around the same curve on the earth?

no

What's the equation for EF at random?

separate each Force into Fx and Fy, then find EFx and EFy, and the Ftotal if needed.

How do you determine Sine

sin(θ) = Opposite / Hypotenuse

How do you determine tangent?

tan(θ) = Opposite / Adjacent

What's Us?

the coefficient of static friction - the roughness of contact area, has no units.

What's apparent weight

the force that an object exerts on the platform of a scale and may be larger or smaller than the true weight mg if the object and the scale have an acceleration a (+ if upward, - if downward). Apparent weight = mg + ma

What are external forces?"

the forces that the environment exerts on the object of interest

What is Uniform Circular Motion?

the motion of an object traveling at a constant (uniform) speed on a circular path

What's inertia and mass?

the natural tendency of an object to remain one of the original two conditions (rest or moving in a constant speed). remain at rest or in motion at a constant velocity. The mass of an object is a quantitative measure of inertia. Measured in KG

Consider two people, one on the earth's surface at the equator and the other at the north pole. Which has the larger centripetal acceleration?

the person at the equator

What is the chance of a light car safely rounding an unbanked curve on an icy road as compared to that of a heavy car: worse, the same, or better? Assume that both cars have the same speed and are equipped with identical tires.

the same

What's a contact force?

they arise from the physical contact between two objects

What is the uniform circular equation?

v =2Pi*r/T period T is the time required to travel once around the circle—that is, to make one complete revolution

A stone is tied to a string and whirled around in a circle at a constant speed. Is the string more likely to break when the circle is horizontal or when it is vertical? Assume that the constant speed is the same in each case.

vertical