# Man on a Flatcar With Ball

• postfan
In summary, the person throws the ball with a speed v2= 18 m/s with respect to the flatcar. The ball leaves his hand at a speed v1= 20 m/s with respect to the ground. The ball moves horizontally as it passes through the hoop at a speed v2= 18 m/s. The hoop is at a height h=4 m above his hand. The person throws the ball with a speed v2= 18 m/s with respect to the flatcar. Let g=10 m/s2 and neglect air drag completely.
postfan

## Homework Statement

A person is riding on a flatcar traveling at a constant speed v1= 20 m/s with respect to the ground. He wishes to throw a ball through a stationary hoop in such a manner that the ball will move horizontally as it passes through the hoop. The hoop is at a height h=4 m above his hand. He throws the ball with a speed v2= 18 m/s with respect to the flatcar. Let g=10 m/s2 and neglect air drag completely. (see figure)

(a) At what horizontal distance x in front of the hoop must the person release the ball? (in meters)

(b) When the ball leaves his hand, what is the direction of the velocity vector of the ball as seen from the flatcar? (angle αcar with respect to the horizontal in degrees)

(c) When the ball leaves his hand, what is the direction of the velocity vector of the ball as seen from the ground? (angle αground with respect to the horizontal in degrees

## The Attempt at a Solution

I found the y component of the initial velocity using the equation 0=v_0*2=2(-10)(4), which I found to be 4sqrt(5). I used this to find the x component of the initial velocity which I calculated to be 2sqrt(61). I found the angle with respect to the boxcar by taking sin^-1=4sqrt(5)/18), angle =29.795 degrees.

To find the time to reach the hoop I used the equation 4=4sqrt(5)-5t^2, t=.8944. Knowing the time and x-component of the velocity I calculated the horizontal distance to be 13.971.

I have no clue how to find the angle relative to the boxcar.

Can someone please check my work on the first 2 parts and how to get the third part? Thanks!

Could you post your equations in symbolic form? I'm not sure where 0=v_0*2=2(-10)(4) is coming from. Are you saying that twice the initial velocity is equal to zero?

I used the equation v=v_0^2+2*a*x for (1) and x=v_0t+.5t^2 for (2).

postfan said:

## Homework Statement

A person is riding on a flatcar traveling at a constant speed v1= 20 m/s with respect to the ground. He wishes to throw a ball through a stationary hoop in such a manner that the ball will move horizontally as it passes through the hoop. The hoop is at a height h=4 m above his hand. He throws the ball with a speed v2= 18 m/s with respect to the flatcar. Let g=10 m/s2 and neglect air drag completely.

It sounds like you have been using set equations without considering the physics of the problem.
Otherwise you'd know how to find the angles.

if the person throws at speed u=v2 (I like to minimize subscripts) and angle θ wrt the flatcar, and the flatcar is moving at speed v=v1 wrt the ground
then :
1. what is the initial horizontal speed ##u_x## wrt the flatcar?
2. what is the initial vertical speed ##u_y## wrt the flatcar?
3. what is the initial horizontal speed ##u_{xg}## wrt the ground?
4. what is the initial vertical speed ##u_{yg}## wrt the ground?
5. what is the initial speed ##u_g## wrt the ground?
6. what is the initial angle ##\theta_g## wrt the ground?
... leave everything as variables - you are writing out equations.

It is best practice to to the algebra before you do the substitutions. If nothing else it makes it easier to troubleshoot your equations. In order to help you we need to see your reasoning too.

Your work for the first two parts seems to be correct. For the third part, you can use the fact that the angle of the velocity vector with respect to the ground is equal to the sum of the angle with respect to the flatcar and the angle of the flatcar with respect to the ground. In this case, the angle of the flatcar with respect to the ground is 0 degrees since it is moving horizontally. Therefore, the angle of the velocity vector with respect to the ground is also 29.795 degrees.

## What is "Man on a Flatcar With Ball"?

"Man on a Flatcar With Ball" is a famous painting by artist Jack Levine. It was created in 1939 and is currently on display at the Museum of Modern Art in New York City.

## What is the significance of this painting?

This painting is considered a satirical commentary on the social and political issues of the time period in which it was created. It reflects the struggles of the working class and critiques the corruption and greed of the upper class.

## What is the medium used in "Man on a Flatcar With Ball"?

The medium used in this painting is oil on canvas. This is a common medium for paintings as it allows for rich colors and textures.

## What inspired Jack Levine to create this painting?

Jack Levine was a social realist painter who was deeply influenced by the struggles of the working class during the Great Depression. He often used his art as a form of social commentary, and "Man on a Flatcar With Ball" was created in response to the economic and political climate of the 1930s.

## What is the meaning behind the title "Man on a Flatcar With Ball"?

The title refers to the central figure in the painting, a man who is seen sitting on a flatcar with a large ball. This symbolizes the burden and struggle of the working class, who are constantly trying to keep up with the demands of their jobs and society, represented by the ball.

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