# Physics 1st year Kinematic world problems. IF you have the time, Thanks

• Mohammed17
In summary, the conversation discusses a kinematics experiment where a student throws a red ball upwards and a blue ball downwards with the same initial speed. The question asks which statements are true about the speed, velocity, and acceleration of each ball right before they hit the ground. The conclusion is that the blue ball will have a greater speed due to experiencing a longer period of acceleration, and the red ball will have a velocity of zero when it passes by its initial position on the way back down.
Mohammed17
Here is the problem that I am having trouble with (It probably is a no brainer, but i am a bit rusty- not a bit actually, a lot!).

Here is the question:
A student stands at the top of a building to perform a kinematics experiment. He throws a red ball directly upwards with an initial speed (Vo). At the same time, he throws a blue ball directly downwards with the same initial speed (Vo). Neglecting air resistance, which of the following statements are true regarding each of the balls, just before they reach the ground?

a) The speed of the blue ball is greater than that of the red ball.
b) The speed of the red ball is greater than that of the blue ball.
b) The two balls have the same velocity.
d) The blue ball has a greater acceleration than the red ball.

I think the answer is a) because since the blue ball is higher than the red ball when it is descending, the blue ball will be affected by the acceleration due to gravity for a longer period of time therefore right before it hits the ground it will have a higher speed. But what I am skeptical about is the last part of the question where it says just before they hit the ground, does that mean they both meet at a given time before they hit the ground or is it talking about each seperately? Because i am assuming that the red ball will hit the ground before the blue ball.

any ideas?

thanks in advance! - Mohammed.

What will the velocity of the red ball be when it passes by it's initial position on the way back down? From this, what can you say about the velocity of the red ball in relation to the blue ball right before it hits the ground?

Note: the blue ball hits the ground before the red ball, but we are examining the velocity of each ball separately just before it hits

If there is no air resistance and you throw the ball up with a certain velocity, it stops turns around and comes back down, what will be the velocity as it passes by the spot you threw it from?

Thanks a lot guys! I had also thought that because they both end up hitting the ground, their velocity becomes zero. Thanks!

Hello Mohammed,

Thank you for reaching out to me for assistance with your kinematics problem. First of all, it is completely normal to feel rusty or unsure about certain concepts in physics. It is a complex and constantly evolving field, so it is important to take the time to review and practice in order to fully understand and apply these principles.

Now, let's take a closer look at the question. You are correct in thinking that the answer is a). This is because the blue ball, being thrown upwards, will have a longer distance to cover before it reaches the ground. This means that it will experience the acceleration due to gravity for a longer period of time, resulting in a higher final speed just before it hits the ground.

To address your concern about the timing of the balls reaching the ground, the question is referring to the moment just before they hit the ground separately. This means that the blue ball will have a higher speed compared to the red ball at that given moment.

I hope this helps clarify the problem for you. Keep up the good work and don't be afraid to ask for help when needed. Good luck with your studies!

## 1. What is kinematics in physics?

Kinematics is the branch of physics that deals with the motion of objects without considering the forces that cause the motion. It focuses on the position, velocity, and acceleration of objects over time.

## 2. How do you solve kinematic problems?

To solve kinematic problems, you will need to identify the given information, such as initial and final positions, velocities, and accelerations. Then, use the appropriate equations of motion (such as the kinematic equations or SUVAT equations) to solve for the unknown variables.

## 3. What are the different types of motion in kinematics?

The three types of motion in kinematics are linear motion (motion in a straight line), circular motion (motion along a circular path), and rotational motion (motion around a fixed axis).

## 4. How is kinematics used in real life?

Kinematics is used in many real-life applications, such as designing and analyzing the motion of vehicles, predicting the trajectory of projectiles, and understanding the movement of celestial bodies in space.

## 5. What is the difference between kinematics and dynamics?

Kinematics deals with the motion of objects without considering the forces that cause the motion. On the other hand, dynamics deals with the motion of objects and how it is affected by forces. In other words, kinematics studies what and how something moves, while dynamics studies why and how something moves.

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