Physics ch 2 Study Guide

20. Velocity can be either positive or negative or zero, depending on displacement. The time interval, ∆t, is always positive. Why?

the time interval will always be positive is because you can't have a negative time. time begins and ends at zero

2. Acceleration is generally defined as the time rate change of velocity. When can it be defined as the time rate change of speed?

Acceleration can be defined as the time rate change of speed when it is going in a straight line. Velocity is measured by change of direction, so if the direction stays constant, the acceleration will be the time rate change of speed.

15. Neglecting air resistance, how does the acceleration of a ball that has been tossed straight upward compare with its acceleration if simply dropped? Explain.

Acceleration due to gravity affects all objects (unless affected by another force) in the same way. So, even though one was tossed up, they still would have equal acceleration because they are both affected by gravity in the same way.

19. If the average velocity of a car is zero in a given time interval, how do you describe the displacement of the car for that interval?

If the average velocity of the car is zero, it means that the cars location at the starting and ending time are the same. For instance, the car can travel around in a circle 5 times; as long as the car ends up at the starting point, the displacement is zero.

3. What is the effect of air resistance on the acceleration of a falling object? What is the acceleration with no air resistance?

The effect of air resistance on a falling object is that as the surface area increases, the object's speed decreases. Acceleration with no air resistance will always be g (9.81m/s^2)

9. Cite an example of something with a constant speed that also has a varying velocity. Can you cite an example of something with constant velocity and varying speed? Defend your answers.

An example of something with constant speed and also has a varying velocity is a car going in a circle at constant speed but it has a varying velocity because it is constantly changing direction. Something cannot have constant velocity and varying speed because constant velocity means constant speed in the same direction.

11. Cite an example of something that undergoes acceleration while moving at constant speed. Can you also give an example of something that accelerates while traveling at constant velocity? Defend your answer.

Any object moving in a circle or along a curve is changing velocity (accelerating) even if its speed is constant, because its direction is changing. Something with constant velocity has both constant direction and constant speed, so there is no example of motion with constant velocity and varying speed.

17. As speed increases for on object in free fall , does acceleration increase also? Defend

As speed increases for objects in free fall, the acceleration does not increase. For free-falling objects always have a constant acceleration of -9.81m/s^2 regardless of its speed or direction.

7. Arron is driving south on a highway. Then, without changing speed, Arron round a curve and drive east. (a) Does his velocity change? (b) Do he accelerate? Explain.

Both his velocity and acceleration change because he changed his direction while turning, which changes velocity. Since acceleration is any change in velocity over a period of time, it is also affected by his turn.

5. For straight-line motion, how does a speedometer indicate whether or not acceleration is occurring?

By showing the change in speed. If the speed increases or decreases, acceleration is occuring.

16. If it were not for air resistance, why would it be dangerous to go outdoors on rainy days?

It would be dangerous to go outside on rainy days if there was no air resistance because the drops of water would gain speed, due to gravity. Air resistance acts as a buffer to slow down the rate of rain drops, therefore without out, it would cause rain to fall down at such a quick rate causing them to fall almost like bullets.

13. Suppose that a freely falling object were somehow equipped with a speedometer. By how much would its reading speed increase with each second of fall? Defend your answer.

It would increase by 9.81 m per second without any external force/air resistance. This answer is proven because that is the speed rate that gravity pulls things back down to earth.

14. For a freely falling object dropped from rest, what is the acceleration at the end of the third second of fall? At the end of the sixth second of fall? Defend your answers.

The acceleration is always going to be 9.81^2 for free-falling objects.

10. Cite an instance in which your speed could be zero while your acceleration is nonzero. Defend your answer.

The instance would be when an object is thrown into the air and it reaches its maximum point where the speed is zero. However, the object still is affected by g (gravity) and has an acceleration of 9.81m/s^2.

18. A ball tossed upward will return to the same point with the same initial speed when air resistance is negligible. When air resistance is not negligible, how does the return speed compare with its initial speed? Explain.

When air resistance isn't negligible, the object will return at a much slower rate compared to its initial speed. When you increase the surface area of an object, the speed decreases.

12. Can you cite an example in which the acceleration of a body is opposite in direction to its velocity? If so, what is your example?

Yes, when a free-falling object is thrown up in the air, its velocity is positive but it is affected by the gravitational pull, which always has an acceleration of -9.81m/s^2 regardless of the object's direction.

4. Can an object reverse its direction of travel while maintaining a constant acceleration?

Yes. For example, a free-falling object undergoes a constant acceleration of 9.81m/s^2, even though the direction changes as it rises and falls

6. Correct your friend who says, "The racecar rounded the curve at a constant velocity of 50 m/s."

You can't have constant velocity when the object changes direction. They mean "the race car rounded the curve at a constant speed of 50m/s."

8. Starting from rest, one car accelerates to a speed of 50 m/s, and another car accelerates to a speed of 60 m/s. Can you say which car underwent the greater acceleration? Why or why not?

You can't tell which car underwent greater acceleration because it doesn't tell how long it took to reach those speeds.

1. When are you most aware of motion in a moving vehicle--when it is moving steadily in a straight line or when it is accelerating? If a car moved with absolutely constant velocity (no bumps at all), would you be aware of motion? Explain.

You would be most aware of motion when the vehicle is accelerating. If a car moved with absolutely constant velocity, we would not be aware of motion because it is going at the same speed and direction.