PHYS: Midterm

What is the REAL force that pulls you toward the outside of a curve when your car makes a tight turn?

Inertia

There is an analogy between rotational and linear physical quantities. What rotational quantities are analogous to distance and velocity?

the rotation angle and angular velocity are the analogy between rotational and linear physical quantities

Race car drivers routinely cut corners as shown in Figure 6.32. Explain how this allows the curve to be taken at the greatest speed.

the second driver has more gravitational curve and also a larger radius. both cars need the maximum of static friction. for car one the sharper the turn is the smaller as well. With that being said he needs the greatest amount of conceptual force.

Explain why it is easier to climb a mountain on a zigzag path rather than one straight up the side. Is your increase in gravitational potential energy the same in both cases? Is your energy consumption the same in both?

the zigzag path is easier to climb up a mountain because the gravitational pull for each step is less for distance, and it requires less force at any instant. When climbing on a straight path, the distance is shortest and the gravitational pull is more, therefore going straight would be more difficult to climb (The zigzag path increases time, which decreases power (P=W/time))

What is the acceleration of a rock thrown straight upward on the way up? At the top of its flight? On the way down?

-9.8m/s/s, -9.8m/s/s, -9.8m/s/s,

Give an example of a nonzero vector that has a component of zero.

An example of a nonzero vector that can have a zero component is best described on a graph. Any nonzero vector along the y-axis has a zero component on the x-axis of a graph, for example (0,10) and (10,0). Both of these coordinates have zero on opposite axes and therefore are nonzero vectors with magnitude and direction.

An American football lineman reasons that it is senseless to try to out-push the opposing player, since no matter how hard he pushes he will experience an equal and opposite force from the other player. Use Newton's laws and draw a free-body diagram of an appropriate system to explain how he can still out-push the opposition if he is strong enough.

According to Newton's Third Law, for every action there is an equal and opposite reaction. This is true for both of the players involved in this scenario, however if there is enough force in one direction that is greater than the other player's force, they will be able to push the weaker player over. As seen in the free-body diagram, as long as the force that is applied (pushing against each other) is greater than the force of friction for one player, that player with the stronger applied force will be able to push the other player over.

The glue on a piece of tape can exert forces. Can these forces be a type of simple friction? Explain, considering especially that tape can stick to vertical walls and even to ceilings.

Adhesive, unlike simple friction, does not require a force like gravity, so it cannot be simple.

What is an elastic collision?

An elastic collision is one that conserves internal kinetic energy.

What is an inelastic collision? What is a perfectly inelastic collision?

An inelastic collision can be defined as a collision in which the energy is not conserved, or the internal kinetic energy changes. A perfectly inelastic collision is a collision in which objects stick together (also known as "perfectly inelastic").

A rock is thrown straight up. What is the net external force acting on the rock when it is at the top of its trajectory?

At the top of its trajectory, a rock thrown straight up will have the external force of gravity (9.8 m/s) acting upon it and drawing it back to Earth.

Is there a real force that throws water from clothes during the spin cycle of a washing machine? Explain how the water is removed.

Centrifugal is not a real force. Inertia pushes the water in a straight path

Which of these is not a fundamental field force?

Drag

A person wins a bar bet by quickly flicking a notecard sitting on a glass from under a quarter so that the quarter goes in the glass without touching it. Which of Newton's Laws did they demonstrate?

First

What properties do forces have that allow us to classify them as vectors?

Forces are classified as vectors because the push or pull action of force has both direction and magnitude. In addition, weight (which is a key contributor to calculate net force) can be classified as a vector because it is the measurement of gravity, which is the down direction.

Under what conditions can a rotating body be in equilibrium? Give an example.

Net external forces must be zero (no acceleration)

Explain, in terms of the properties of the four basic forces, why people notice the gravitational force acting on their bodies if it is such a comparatively weak force.

Gravity is a weak force, and people only notice it because it is always attractive. We may observe this weak force by counteracting the force by jumping, climbing, lifting, etc. This is a weaker force than electromagnetic energy, which we do not notice in everyday life because atoms are miniscule particles that we cannot observe yet would not exist without.

Two friends are having a conversation. Anna says a satellite in orbit is in freefall because the satellite keeps falling toward Earth. Tom says a satellite in orbit is not in freefall because the acceleration due to gravity is not 9.80 m/s2size 12{9 "." "80"`"m/s" rSup { size 8{2} } } {}. Who do you agree with and why?

I agree with Anna's point that the satellite in orbit is in freefall. The satellite is not falling at the rate of 9.8m/s2, however freefall can occur in other forces of gravity. For example, an object can experience the action of freefall on a different planet (ex. Mars), which is why the satellite in this scenario is very well experiencing freefall, just with a different force than the force of Earth's g.

If an airplane pilot is told to fly 123 km in a straight line to get from San Francisco to Sacramento, explain why he could end up anywhere on the circle shown in Figure 3.51. What other information would he need to get to Sacramento?

If the pilot was only given the directions to go 123 km in a straight line to get from San Francisco to Sacramento, the plane could end up anywhere on the circle because a direction was not given. Since the radius of the circle is 123 km with San Francisco at the center, the plane could end up anywhere on the outside of the circle because the plane would need to go North East.

Explain in terms of impulse how padding reduces forces in a collision. State this in terms of a real example, such as the advantages of a carpeted vs. tile floor for a day care center.

Impulse is a product of force and the amount of time the force is applied. If Impulse magnitude is held constant, increasing time of collision will reduce force applied.

How are inertia and mass related?

Inertia and mass are directly proportional because inertia is measured from an object's mass. This means that the more inertia an object has, the more mass it has and vice versa. Inertia is the measurement of resistance and how an object resists change in its state of motion. Therefore, a more massive object is more likely to resist change which means there is more inertia.

If someone is riding in the back of a pickup truck and throws a softball straight backward, is it possible for the ball to fall straight down as viewed by a person standing at the side of the road? Under what condition would this occur? How would the motion of the ball appear to the person who threw it?

It would be possible for the ball to appear as falling straight down by the person standing on the side of the road as long as the speed of the ball being thrown is at the same speed as the truck. The ball would have to be thrown with the same magnitude and velocity as that of the truck in order for the ball to appear falling straight down as well. In addition, to the person in the truck that threw the ball, it would look like it was moving away from the person at whatever speed they threw it.

How are inertia and mass related?

Mass is a way to quantify the amount of inertia an object has.

What is the relationship between weight and mass? Which is an intrinsic, unchanging property of a body?

Mass is an intrinsic, unchanging property that is the measure of how many atoms make up an object. Weight is a measurement of the force acting upon an object based on the gravitational forces at that place. For example, a human will have the same mass (or atomic makeup) on Earth and the Moon. However, that same human would weigh more on Earth than the Moon because the force of gravity on Earth (9.8 m/s) is larger than the forces acting upon that person on the Moon.

What is the relationship between weight and mass?

Mass is constant, weight can vary from place to place.

Under what circumstances is momentum conserved?

Momentum is conserved in all situations except for the book examples of impulse, linear momentum, and force. In order to determine how the momentum is conserved, we must take the size of the system into account. Depending on how we define the system and surroundings, we are able to identify if we can "see" the conservation. For example, if a child crashes their bike into a curb, there is a force on them that causes them to bounce backwards. However, the Earth also recoils and conserves momentum because the force of the child's bike goes through the curb and into the Earth's surface. Since the Earth is larger than the curb the child hit with their bike, the recoil is less obvious and harder to observe than the crash into the curb.

Can an object's velocity be constant yet it's acceleration not be zero?

No

Are the astronauts on the international space station weightless?

No, they are in freefall.

Give an example of something we think of as work in everyday circumstances that is not work in the scientific sense. Is energy transferred or changed in form in your example? If so, explain how this is accomplished without doing work.

One example of work in the sense of everyday life is writing an essay. This is not "work" by the scientific definition because scientific work involves the relationship between energy being transferred. Since writing a paper does not involve a physical force, but instead involves mental strength which is not transferring a form of energy, this is not "work" as defined in the field of science.

Athletes such as swimmers and bicyclists wear body suits in competition. Formulate a list of pros and cons of such suits.

Pros: A faster performance would result because of the reduced drag of the outside forces on the athlete (ex. Water or wind). Cons: Not a fair competition and jeopardizes the integrity of the race by giving the athlete an additional advantage against the obstacles of their sports.

An object that has a small mass and an object that has a large mass have the same momentum. Which object has the largest kinetic energy?

Recalling that mass and velocity are inversely proportional, the object with the larger mass has a smaller velocity. Keeping in mind that the objects have the same momentum, the smaller object will have the larger Kinetic Energy.

When we step forward, we are accelerated forward much more than the Earth is accelerated backward. This demonstrates which of Newton's Laws?

Second

What three factors affect the torque created by a force relative to a specific pivot point?

Torque (𝜏) is affected by three forces relative to a specific point. These include: The distance from the pivot point to the point where force is applied (𝑟), the magnitude of the force (𝐹), and the angle between the force and vector directed from the application to the pivot point (𝜃).

Certain types of dinosaurs were bipedal (walked on two legs). What is a good reason that these creatures invariably had long tails if they had long necks?

Since these dinosaurs had long necks, this caused their center of mass to be higher. If there is a slight movement of their neck, the movement causes an imbalance or unstable equilibrium. Therefore, it was important that they have a long tail to help balance their necks by moving in the opposite direction.

Name the two kinds of friction and which one imparts a higher force.

Static and Kinetic. Static imparts higher force.

To simulate the apparent weightlessness of space orbit, astronauts are trained in the hold of a cargo aircraft that is accelerating downward at 𝑔. Why will they appear to be weightless, as measured by standing on a bathroom scale, in this accelerated frame of reference? Is there any difference between their apparent weightlessness in orbit and in the aircraft?

The astronaut will appear weightless because the aircraft is counteracting the force of gravity with acceleration. When the scale is on Earth, the force of gravity is forcing the scale down, while the ground provides an equal/opposite force holding the scale in place, therefore allowing the scale to stay in place on the ground and measure weight added to the force of gravity acting upon it. When the aircraft is in orbit and away from Earth's gravitational pull, the scale and the astronaut are no longer being forced downward by the force of gravity and there is no equal/opposite force pushing the scale from the floor. So, the scale will not be able to record weight when there is an absence of gravitational pull acting upon it and the astronaut, therefore making them "weightless".

The person in Figure 7.32 does work on the lawn mower. Under what conditions would the mower gain energy? Under what conditions would it lose energy?

The lawnmower in Figure 7.32 gains energy from the person pushing it. If/when a person pushes the lawnmower at a constant speed, the energy transferred to the lawnmower and the friction of the person pushing the lawnmower causes work in the form of heat being given off. The lawnmower would lose energy if the person stops pushing the lawnmower forward or slows down their pace.

Mechanics sometimes put a length of pipe over the handle of a wrench when trying to remove a very tight bolt. How does this help? (It is also hazardous since it can break the bolt.)

The length of pipe placed over the handle of a wrench by a mechanic is used to lengthen the tool, therefore increasing the torque (or rotational force) applied to loosen the bolt.

Does the work you do on a book when you lift it onto a shelf depend on the path taken? On the time taken? On the height of the shelf? On the mass of the book?

The path that is taken to lift a book off of a shelf does not affect the work done because displacement does not depend on a path. In addition, time is not taken into effect for the equations of work and therefore does not affect the work in this scenario. The mass and height of the shelf does matter. The height is directly linked to displacement and mass measures the force against gravity, which are both components of calculating work.

Rockets operate by pushing lots of gas particles downward, which results in the rocket being pushed upward. Which of Newtons Laws is demonstrated by this effect?

Third

Most electrical appliances are rated in watts. Does this rating depend on how long the appliance is on? (When off, it is a zero-watt device.) Explain in terms of the definition of power.

Watts (Joules/s) measures power and does not depend on how long the appliance is on

During a lecture demonstration, a professor places two coins on the edge of a table. She then flicks one of the coins horizontally off the table, simultaneously nudging the other over the edge. Describe the subsequent motion of the two coins, in particular discussing whether they hit the floor at the same time.

When the coins leave the professor's hand, the only force acting upon the coin in the up and down direction is gravity. Despite one moving horizontally, there is the same amount of force due to gravity (g) on both of the coins therefore they will hit the ground at the same time after being dropped simultaneously.

The gravitational force on the basketball in Figure 4.6 is ignored. When gravity is taken into account, what is the direction of the net external force on the basketball—above horizontal, below horizontal, or still horizontal?

When the gravity is taken into effect, the net external force will be below horizontal.

Describe the energy transfers and transformations for a javelin, starting from the point at which an athlete picks up the javelin and ending when the javelin is stuck into the ground after being thrown.

When the javelin is on the ground there is no energy whatsoever, when the thrower picks it up there is energy being done (specifically gpe). When the thrower goes to throw the javelin there is kinetic energy being done. When the javelin hits the ground it applies a force on the javelin which stops the kinetic energy.

Explain the mechanical advantage of a wheelbarrow and how it explains why moving a heavy load is easier with a wheelbarrow.

When using a wheelbarrow, you are able to lift heavier loads due to the force distribution. The mechanics of a wheelbarrow involve the input force, the output force, and the force on the pivot. Since the output force (or load) is between the pivot (wheel's axle) and the input force, the output force is greater than the input force. Therefore, these mechanics make it possible to lift more weight than you could with your body alone.

Can a nonzero vector have a component of zero?

Yes, if it has magnitude in 1 axis only, the magnitude of the component in the other axis must be zero.

A car's odometer measures

distance

When deciding if an object is in motion, which of these should be considered first?

frame of reference

What is an example of being precise, but not accurate?

measurements that are all close to one another, but not close to the actual length

When analyzing projectile motion,

motion in the 2 axes should be analyzed separately.

The difference between a scalar and a vector is

scalar has magnitude, vector has magnitude and direction

A model is

simpler than the real world thing it represents.

Angular velocity is analogous to what straight line value?

velocity

What 2 factors affect centripetal acceleration and how do they affect it?

velocity directly and radius inversely