HOMEWORK QUESTIONS:WEEK 1

Jacob says acceleration is how fast you go. Emily says acceleration is how fast you get fast. They look to you for confirmation. Who's correct?

After reviewing Chapter 3 and notes from class , speed can be defined as the distance covered per unit of time. In simple terms, how fast you go. Speed=distance /time. Acceleration can be defined as how quickly and in what direction velocity changes. In simple terms, acceleration is the change in speed whether it be going faster or slowing down. Acceleration= change of velocity/ time interval. So, Emily would be correct. An example would be driving in a car and traveling from 25-45 mph in 30 seconds.

What is the acceleration of a car that moves at a steady velocity of 100 km/h for 10s? Explain your answer.

After reviewing chapter 3, it indicates that acceleration could be defined as change. It could be changes in both direction and speed. The question above states that the car is moving at a steady velocity which tells me that the car is not accelerating because there is no change. Therefore the car's acceleration would be zero. The acceleration is zero, the car is moving at a constant speed of 100 km/h, the change of speed , not the speed itself, is 0 km/h, therefore by definition, acceleration = 0 (km/h) / 10 (s) = 0 (km/h per second). Usually the challenging part of understanding acceleration is that it is the change of speed, not the speed itself, the two concepts are different.

Galileo experimented with balls rolling on inclined plans of various angles. What is the range of accelerations from angles 0 to 90 degrees (from what accelerations to what)?

After reviewing notes from last class and chapter 3 in the text, the formula i used to determine the speed for this was 10m/s^2 (9.8 m/s^2). Therefore, since it is getting doubled, I believe the acceleration from angle 90 would be at 180 seconds.

Boy Bob stands at the edge of a cliff (as in Figure 3.8) and throws a ball nearly straight up at a certain speed and another ball nearly straight down with the same initial speed. If air resistance is negligible, which ball will have the greater speed when it strikes the ground below?

Although the ball dropped straight down will reach the ground first, the ball thrown upwards will hit the ground at a greater speed. This occurs because, with every second, the ball accelerates 10 meters, giving the ball thrown upward a higher acceleration than the ball thrown straight down at a shorter distance.

As speed increases for an object in free fall, does acceleration increase also?

As speed increases for an object in free, acceleration also increases. When an object is in free fall, the object is free of any restraints that are friction with the air and is only falling under the works of gravity. As each second pass, the object gains 10m/s which is the acceleration.

Why would a person's hang time be considerably greater on the Moon than on Earth

Gravity determines how fast a person falls, and it also influences the acceleration before they hit the ground increasing the speed with each second. Hang time is a phrase that is often times used to describe the time before a person enters free fall and falls back to the ground. Hang time is the time it takes for you to rise and fall. This idea is exemplified when basketball players jump in the air and they have a very short amount of time in the air before they touch the ground again. This is done because force is applied from your feet to the ground, and the greater the force the higher the jump and the longer you are in the air. However after you leave the ground, the speed you had going up is decreased because of gravity and you begin to accelerate downwards at the same rate. The hang time on the moon is considerably greater because there is significantly less of a gravitation pull than it would be on earth. To put it into perspective the rate at which an object accelerates or g is 9.8 m/s2 on earth, but on the moon the g value is 1.6 m/s2.

While rolling balls down an inclined plane, Galileo observes that the ball rolls 1 cubit (the distance from elbow to fingertip) as he counts to 10. How far will the ball have rolled from its starting point when he has counted to 20?

I reviewed the information under the heading " Acceleration on Galileo's Inclined Planes," and examples from for question 68. 1 cubit = 10 counts. If Galileo rolls the ball to 20 counts, it would equal to 2 cubits. Speed is proportional to time, v=at, distance is proportional to time squared, d=0.5at^2, in twice the time, the ball will roll four times as far. The three concepts, distance, speed and acceleration are related but also different. The question was about the distance rather than speed.

Suzie Surefoot can paddle a canoe in still water at 8 km/h. How successful will she be canoeing upstream in a river that flows at 8 km/h?

If Suzie Surefoot can paddle 8km/hr upstream in a canoe in still water at 8km/hr, then she wont be very successful because she would be technically traveling at 0km/hr. The upstream speed is canceled by the downstream flow rate. She isnt going anywhere if she paddles at the same flow rate of the river. Therefore she is stuck in the river and needs to increase her speed if she wants to go upstream.

If air resistance can be ignored, how does the acceleration of a ball that has been tossed straight upward compare with its acceleration if simply dropped?

If air resistance is ignored, the acceleration of a ball that has been tossed straight upward or dropped would be the same. Whether the ball is moving upward or downward, its acceleration is 10 m/s2. The question is about the acceleration, not the speed. The acceleration is the same no matter which way the object is tossed. However the speed can be different in magnitude as well as direction. It is important to distinguish the two concepts.

Suppose that the freely falling object in the preceding exercise were also equipped with an odometer. Would the readings of distance fallen each second indicate equal or different falling distances for successive seconds?

In the previous question, if an object is free falling, it is free of air drag. The speed would remain constant because the acceleration would not increase since it is a constant of 10 (m/s2). This would show that each second the readings of distance fallen would remain the same each time if you are going the same speed for the entire distance. If the speed was faster, the object would have traveled a greater distance, or if the speed was slower, the object would have traveled not as far. Therefore, the speed is constant, so the distance should be equal each second.

You're traveling in a car at some specified speed limit. You see a car moving at the same speed coming toward you. How fast is the car approaching you, compared with the speed limit?

The answer to this question is that the approaching car is moving twice the speed limit. The speed of your car and the speed of the other car are added together. This is true because when you think about speed, it all depends on your viewing position. Let's say you are driving at 30 mph and the vehicle driving towards you is going at 30 mph as well. You will observe that the car approaching is moving faster than you, but in reality you are going at the same speed

Jo, with a reaction time of 0.2 second, rides her bike at a speed of 6 m/s. She encounters an emergency situation and "immediately" applies her brakes. How far does Jo travel before she actually applies the brakes?

Total distance traveled equals the velocity times the time it takes to travel that distance. Since Jo was traveling at a velocity of 6 m/s and her reaction time was 0.2 second, Jo traveled 1.2 meters before she actually applied the brakes. I simply rearranged the speed equation shown below: SPEED=DISTANCE/TIME The question is asking for the distance that Jo traveled, so I rearranged the equation to "speed x time = distance" to solve the problem and got the same answer, 1.2m

Vertically falling rain makes shared streaks on the side windows of a moving automobile. If the streaks make an angle of 45 degrees, how does the speed of the automobile compare with the speed of falling rain?

We need to use properties of a line, and the idea of velocity. Velocity is combines speed and the direction of motion. The rain streaks pointing down, and the moving automobile moving in a horizontal direction are perpendicular to one another. If the rain velocity changes at a 45 degree angle, both the speed of the falling rain and a moving automobile remain constant. In other words, both the car and rain streaks are moving in the same direction, and the same sped. Their paths are on the line, only one straight path between two points. It doesn't matter if these two lines are parallel or perpendicular.

One airplane travels due north at 300 km/h while another travels due south at 300 km/h. Are their speeds the same? Are their velocities the same? Explain.

n terms of speed, Yes, the airplanes are traveling at the same speed of 300 km/h, one towards the north and the other towards the south. Speed is the ratio of distance traveled to time taken, or, speed=distance/time. Using the relation between distance, time, and speed, we can see that both planes have the same speed. In terms of velocity, Velocity is a vector representing speed and direction. The planes are traveling in two different directions, therefore they are not the same. The speed is equivalent to each other but their velocities the negations of each other with one going north and the other going south. Changing velocity is if the speed or the direction changes but in this instance, the directions are both different. Therefore they are not the same in their velocities but the same in their speeds.