Kinematics Problem: Ball Thrown from 84m Window with 32.2m/s Velocity

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In summary, a simple kinematics problem involves studying motion without considering forces and typically involves calculating position, velocity, and acceleration. These problems can be solved using the SUVAT equations and the key variables are position, velocity, acceleration, and time. An example problem involves calculating the position of a ball after 5 seconds when thrown off a building with an initial velocity of 20 m/s. Simple kinematics problems are important because they allow us to understand and predict motion in various real-world situations.
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sz1989
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Homework Statement


I throw a ball vertically out of a 84meter high window with an intial velocity of 32.2m/s. How many seconds until the ball hits the ground


Homework Equations





The Attempt at a Solution

 
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  • #2
You have to give us an idea of what you have tried to solve this problem before anyone will help you.

Apparently you understand that this is a kinematics problem, so start from there. What Kinematic equations do you know, and what one do you think will apply to describe this situation?
 
  • #3


Using the equation for displacement in kinematics, we can calculate the time it takes for the ball to hit the ground. The equation is given by:

d = vi*t + 1/2*a*t^2

Where d is the displacement (in this case, the height of the building), vi is the initial velocity, a is the acceleration due to gravity (9.8m/s^2), and t is the time.

Plugging in the given values, we get:

84m = 32.2m/s * t + 1/2 * 9.8m/s^2 * t^2

Simplifying and rearranging the equation, we get a quadratic equation:

4.9t^2 + 32.2t - 84 = 0

Solving for t using the quadratic formula, we get two possible solutions: t = 2.77s or t = -6.07s. Since we are looking for the time it takes for the ball to hit the ground, we can discard the negative solution. Therefore, it will take approximately 2.77 seconds for the ball to hit the ground.
 

What is a simple kinematics problem?

A simple kinematics problem is a type of physics problem that involves the study of motion without considering the forces that cause the motion. It typically involves calculating the position, velocity, and acceleration of an object over a given time period.

How do you solve a simple kinematics problem?

To solve a simple kinematics problem, you can use the equations of motion, which relate an object's position, velocity, and acceleration to each other. These equations are often referred to as the "SUVAT" equations and can be solved using algebraic techniques.

What are the key variables in a simple kinematics problem?

The key variables in a simple kinematics problem are position (x), velocity (v), acceleration (a), and time (t). Other variables that may be involved depending on the problem include initial velocity (u) and displacement (Δx).

Can you provide an example of a simple kinematics problem?

Sure, here's an example: A ball is thrown off a 10-meter high building with an initial velocity of 20 m/s. What is the ball's position after 5 seconds? To solve this, we can use the equation x = ut + ½at², where x is the final position, u is the initial velocity, t is the time, and a is the acceleration (which we can assume to be -9.8 m/s² due to gravity). Plugging in the values, we get x = (20 m/s)(5 s) + ½(-9.8 m/s²)(5 s)² = 50 m - 122.5 m = -72.5 m. Therefore, the ball's position after 5 seconds is -72.5 meters from the ground (or 10 - 72.5 = -62.5 meters from the top of the building).

Why are simple kinematics problems important?

Simple kinematics problems are important because they allow us to understand and predict the motion of objects without considering the forces involved. This can be useful in many real-world situations, such as designing vehicles, analyzing sports movements, or predicting the path of a projectile.

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