Question on relative motion and circular motion.

In summary, the conversation discusses two physics problems that the speaker is struggling with. The first problem involves a science student throwing a ball while riding on a train and the professor observing its motion. The second problem involves a race car on a circular track and finding the angle of total acceleration when it completes 7.75 laps. The speaker is seeking guidance in solving these problems and mentions a similar problem in the book for reference. However, without additional information, the problems cannot be solved.
  • #1
SilverLx
5
0
Hey guys, I've been working on this physics for a few hours, and feel like I am just missing a key point. At first I felt that the problem was missing data, until in the same section I found another that I felt the same. Now I feel like I'm missing a concept or two.

The first problem I have having issues with is:

A science student is riding on a flatcar of a train traveling along a straight horizontal track at a constant speed of 10.5 m/s. The student throws a ball into the air along a path that he judges to make an initial angle of 60.0° with the horizontal and to be in line with the track. The student's professor, who is standing on the ground nearby, observes the ball to rise vertically. How high does she see the ball rise?

Now, I see that the train is moving at 10.5 m/s, so although the student throws the ball at the angle of 60.0 degrees to the horizontal, the professor see's the ball's velocity as 10.0 m/s + the vector components at which the student throws the ball? Please guide me in the right direction.


As for my second problem:

A race car starts from rest on a circular track. The car increases its speed at a constant rate at as it goes 7.75 times around the track. Find the angle that the total acceleration of the car makes with the radius connecting the center of the track and the car at the moment the car completes its trip of 7.75 times around the circle.


As for this problem, I am almost at an utter loss. Any help would be greatly appreciated, and I am by no means trying to get answers, just a general push in the right direction. Thanks in advance for your time.
 
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  • #2
Heh, just an update, finally figured out the first one :). ANy help with the second would be appreciated!
 
  • #3
anyone :frown:
 
  • #4
SilverLx said:
As for my second problem:

A race car starts from rest on a circular track. The car increases its speed at a constant rate at as it goes 7.75 times around the track. Find the angle that the total acceleration of the car makes with the radius connecting the center of the track and the car at the moment the car completes its trip of 7.75 times around the circle.
In general, something going in a circle could have both a tangential and radial component of acceleration. However, since you are given no information about the speed of the car or the radius of the track, I don't see how you can solve this one.
 
  • #5
alright, thanks. In the book there was a similar problem, that asked what's the angle if it goes around once, and they said tan(1/4pi) = 4.55° is the answer. Definitely confused on this one..
 
  • #6
SilverLx said:
In the book there was a similar problem, that asked what's the angle if it goes around once, and they said tan(1/4pi) = 4.55° is the answer. Definitely confused on this one..
That answer would make sense if the car made it around in one second. Without that additional information, the problem cannot be solved.

Are you sure you are presenting these problems exactly as given?
 
  • #7
Yeah I am, That's compied an pasted from webassign
 

1. What is the difference between relative motion and circular motion?

Relative motion refers to the motion of an object in relation to another object, while circular motion refers to the motion of an object around a fixed point or axis.

2. How do you calculate the speed of an object in circular motion?

The speed of an object in circular motion can be calculated by dividing the distance traveled by the time it takes to travel that distance. This is also known as the tangential speed or linear speed.

3. What is centripetal force and how does it relate to circular motion?

Centripetal force is the force that keeps an object moving in a circular path. It is always directed towards the center of the circle and is required for an object to maintain circular motion.

4. Can an object have both relative and circular motion at the same time?

Yes, an object can have both relative and circular motion at the same time. For example, a car moving in a circular track while also moving relative to another car on the same track.

5. How does the radius of a circle affect the speed of an object in circular motion?

The speed of an object in circular motion is directly proportional to the radius of the circle. This means that as the radius increases, the speed also increases, and vice versa.

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