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Chapter 7 Review Questions

- Chapter 13 contains answers and explanations.

- There is an object of mass 2 kg with a linear momentum of 6 km/s.

- Find the average strength of the force applied to the box.

- One of the objects is moving with a speed of 2 m/s and the other is moving with a speed of 5 km/s.
- Find the speed of the objects after the collision if the collision is inelastic.

- The mass of Object 2 is twice that of Object 1 and it is initially at rest.

- Two objects collide and separate.

- Two carts are sitting at rest on a table.
- One cart is pushed off the other by the teacher.

- The mass of Object 1 is half that of Object 2.

- The collision is strong.

- The wooden block is suspended from a horizontal support by cords.
- The block swings upward as a result of the perfectly inelastic impact of a bullet hitting it.

- There is a change in momentum.

- A system with no external forces has a conserved quantity of momentum.

- A coordinate system can be created.

- Sometimes you have to rebuild in the end.

- Since man has looked up to the stars, we have always tried to understand why they move the way they do.
- The stars and planets make elliptical circles, which is against the First Law in which objects will continue to move straight.
- The answers explained motion in a linear fashion.
- Our motion became parabolic when we added a second dimension.
- When objects begin to move in a circular motion will be explored.
- We will have a better understanding of the Moon's position around the Earth.

- The object's speed around its path should be constant.
- Although the speed may be constant, the direction of the velocity is always changing.
- There must be acceleration since the velocity is changing.
- This acceleration does not change the speed of the object, it only changes the direction of the velocity to keep it on its path.
- The object would move off in a straight line if there wasn't a force.

- The figures are below.
- There is a figure on the left that shows an object moving along a circular trajectory.

- The object's path is always tangential to the velocity vector.
- The magnitudes are the same.

- Most objects don't undergo uniform circular motion.
- They follow ellipticals with different speeds.

- This won't be tested for the AP physics 1 exam.

- An object moving at constant speed in a circular path is undergoing uniform circular motion.

- The magnitude of the force is given by this equation.
- The force that produces centripetal acceleration points to the center of the path.

- Centrifugal force is not a real force.
- The net force from the physical forces on the object is called capillary force.

- Identifying what forces produce the centripetal acceleration is the first thing to do in a problem like this.
- This is a horizontal circle.

- The unit has changed from 80 cm to 0.80 m.

- The centripetal force is provided by static friction.
- The centripetal force needed to keep him running in a circle would increase if the radius of the arcs were smaller.
- He would slip if the centripetal force increased enough.

- The speed of the car is 15 m/s at the very top of the circle, where the people are upside down.
- If the diameter of the loop is 40 m and the total mass of the car is 1,200 kg, find the magnitude of the normal force by the track on the car at this point.

- There are two forces acting on the car at its topmost point, both of which point downward.
- The normal force is directed downward by the surface of the track.

- Force tells an object how to move.
- The car would fall straight down if it had zero velocity at this point.

- The normal force pushes ninety degrees to the surface, even though the gravity still points downward.
- The forces are against one another.
- The centripetal force is still provided by the combination of these two forces.
- We will make anything that points toward the center of the circle positive and anything that points away from the circle negative, because the centripetal acceleration points inward.

- You would feel little force between you and the seat at the top of the loop, but you would feel a big slam at the bottom of the loop.

- The strength is proportional to the product of the objects' mass and the distance between them as measured from center to center.

- The pulling force is gravity.

- 2-on-1 act along the line that joins the bodies and form an action/reaction pair.

- The law was published more than a hundred years ago.
- The mass of the Earth and the radius of the Earth can be used to calculate gravity.

- The mass of the Earth is determined by the radius of the Earth.

- From above the North Pole, you can see the Earth.

- It is possible to recognize the relationship between variables in formulas.

- The centripetal force is provided by N.

- The difference is so small that it can usually be ignored.

- Satellites are often parked above Earth's surface.
- The satellites have the same position on Earth's surface because they have the same amount of time in the air.
- Determine the altitude that a satellite has to be above the equator.

- The answer is that the Earth pulls.

- Any object at the same distance from the Earth as the moon must move at the same speed.

- There are questions about banking on the AP physics 1 exam.
- Engineers often use banked curves to design and build roads.

- Banking allows for cars to travel around a curve at or below the posted speed limit, without relying on the tires and road.

- The curve is banked at 11.8 degrees if the radius of curvature is 60 m.

- The centripetal force that the car experiences as it rounds the curve is produced by the horizontal component of the normal force.

- The recommended speed is 40 km/hour.

- We covered objects that move in a circular motion.
- Taking those objects and spinning them is the next part of this chapter.

- There were previous equations where objects were moved in a linear orientation.
- We need a new set of equations that are similar to the physics of linear motion.

- An object's mass is its resistance to acceleration.
- The harder it is to change an object's speed, the more inertia it has.
- The greater the inertia, the greater the force that is required in order for an object to be moved.
- If the same force is applied on both objects, Object 1 will experience a smaller acceleration.

- The force, mass, acceleration, and velocity are put in the linear model.

- The relationship between the three rotational parameters and the linear parameters will be explored.

- There are some basic definitions.

- A toy car is going around a circle.

- If you follow the path of the car, you will find that your fingers are counterclockwise.
- The direction of your thumb is determined by your thumb.
- It points out something on the page.

- Many of the equations reflect linear equations.

- Four children are on a carousel.

- The objects were treated as a single particle in the preceding chapters.
- The force is being delivered at a single point on the object.

- Imagine a bunch of experiments.
- We walk into a large room with a hammer and a small light.
- The light will be attached to the end of the hammer in the first experiment.
- We throw the hammer across the room after turning off the light.

- We repeat the experiment again.
- The small light should be attached to the head of the hammer.
- We turn off the light, throw the hammer across the room, and trace the path of the hammer.

- There was something important about that point.

- The one point that gave a smooth path was the only one that gave spiraled trajectory.
- If we place that point on our fingers, we can see that the hammer is horizontal with the floor.

- The center of mass is this point.
- It is possible to say that the center of mass is the point at which all the mass of the object can be concentrated.

- The center of mass is the geometric center of the object.

- The center of mass is motionless as every other point moves around it.

- Pick a location that is convenient.

- The formula above can be used to calculate the center of mass.

- The stick matters.
- If the stick has mass, it must be taken into account to determine its center position.

- We could either palm the ball or put our hands on the opposite side of the ball and push one hand forward and the other backward.
- In both cases, we need to exert force to make the object's center of mass accelerate.
- We need to exert a Torque in order to make an object spin.

- The measure of a force's effectiveness is called Torque.
- Something must have a Torque if it starts to spin after being at rest.
- If an object is spinning, something has to exert a Torque to stop it.

- The systems that can spin have a "center" of turning.
- While the rest of the object is rotating, the point that does not move becomes the center of the circle.
- There are many different terms used to describe this point.

- Students have difficulty understanding the topic of Torque.

- There is a door with a pivot point on the left side of the drawing.
- Some examples can be tried at home on a door to get a better understanding.

- The door will close the fastest in the first situation.

- In both situations, the door will close the fastest.
- The door will not close in situation 3.

- If you try this at home, you will see that it will be easier to close the door if you push it like Situation 2.

- There were a few points that mattered when trying to close the door.
- The amount of force used to close the door mattered.
- The angle in which we pushed the door mattered.
- In scenario 3, the place in which we pushed mattered.

- Our force's effectiveness at rotating was determined by a few factors.

- This is a cross product between your force and your radius.

- The unit is called a newton-meter.

- Torque is not a force because it is not in newtons.
- There was a force being applied to the door straight into the pivot point.
- The force was not enough to close the door.
- It's the equivalent of force in trying to accelerate something.

- A newton-meter became a joule in the previous chapter.
- This isn't the case with Torque.

- Torque problems can involve putting systems in equilibrium.

- A student pulls down a rope with a force of 40 N and a pulley of 5 cm.

- The two forces produce a Torque, but they don't like each other.
- The Torque of F1 is counterclockwise and the Torque of F2 is counterclockwise.
- Imagine the effect of each force if the other wasn't there.

- It's important to balance one force's effectiveness at turning something clockwise with another force's effectiveness at turning it counter-clockwise.

- The wall is connected to the bar's center by a wire.

- The wall on the bar exerts contact force.
- The components are sin 55deg.

- When using center-of- mass, some problems are easier than others.

- You can choose which one is easier.

- This system can't be solved as is.
- The second condition for equilibrium requires that the sum of the Torques about any point is zero.

- cot 55o is what we use here.

- We can put together the pieces of making an object spin now that we've studied Torque and rotation.
- The moment of inertia is the tendency of an object in motion to rotate until acted upon by an outside force.

- We are taking a ball at rest and speeding it up, which is rotational acceleration.
- A force is needed to achieve this.
- In terms of inertia, Torque is required.
- We need to apply a force that works.

- Some key relationships are made by this equation.
- The larger the inertia, the smaller the value for an object.
- It will be more difficult to rotation Object 1 than it will be to rotation Object 2.
- If the same Torque is applied to both objects, Object 1 will undergo a smaller rotational acceleration.

- There is more to it than the object's mass.
- There are two objects that have the same mass.
- How the mass is distributed in an object affects rotational inertia.

- The greater the rotation inertia, the farther away the mass is from it.

- Imagine a barbell with weights near each end and an identical barbell with weights near the middle of the bar.
- The barbells have the same mass, but their inertias are different.
- The first barbell has its attached mass farther away from the axis of rotation than the second barbell.
- It was more difficult to rotation the first barbell than the second one.

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