# What's the speed of ball when travelling over the fence?

• Hoyin
In summary, the conversation discusses a problem in which two girls play baseball in a park and the ball travels over a 4-meter high fence with a speed of 20.0 m/s. The problem asks for the speed of the ball after losing half of its energy to air resistance. The correct solution involves reducing the initial kinetic energy by half.

## Homework Statement

Two girls are playing baseball in a park. The batter hits the 400-g ball with a speed of 20.0 m/s. It travels over the park's fence that is 4.00 m high. Assuming that the ball loses half of its energy to air resistance, at what speed does the ball travel over the fence?

Ek = 0.5*m*v^2
Ep = m*p*h

## The Attempt at a Solution

0.5*(0.4Kg)*(20 m/s)^2 = 0.5 [(0.4Kg)(9.81 m/s^2)((4m) + 0.5(0.4Kg) Vf^2]

Have another think about the first 0.5 on the right of the =.

Hoyin said:
0.5*(0.4Kg)*(20 m/s)^2 = 0.5 [(0.4Kg)(9.81 m/s^2)((4m) + 0.5(0.4Kg) Vf^2]

You're line of thinking is correct. Just stress on which energy needs to be reduced by half.

I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.

Hoyin said:
I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.
That's not what you've done in your equation. Check again.

Hoyin said:
I tried reduce the Kinetic energy by half, but the answer is incorrect. Thanks.
Which term in your equation represents the initial KE? Where is that multiplied by one half?

## 1. What factors affect the speed of a ball when travelling over a fence?

The speed of a ball when travelling over a fence is affected by several factors including the initial velocity of the ball, the angle at which it is thrown or hit, air resistance, and the height and distance of the fence.

## 2. Can the speed of a ball when travelling over a fence be calculated?

Yes, the speed of a ball when travelling over a fence can be calculated using the equation: v = √(2gh), where v is the speed, g is the acceleration due to gravity, and h is the height of the fence.

## 3. Does the material of the fence affect the speed of the ball?

Yes, the material of the fence can affect the speed of the ball. A fence with more give or flexibility, such as a chain-link fence, may slow down the ball more compared to a solid and rigid fence.

## 4. How does the speed of a ball when travelling over a fence differ from its initial speed?

The speed of a ball when travelling over a fence will likely be slower than its initial speed due to the effects of air resistance and gravity. The height and distance of the fence will also play a role in determining the final speed of the ball.

## 5. Is there a maximum speed that a ball can reach when travelling over a fence?

Yes, there is a maximum speed that a ball can reach when travelling over a fence. This is determined by the initial velocity of the ball, the angle at which it is thrown or hit, and the height and distance of the fence. However, factors such as air resistance and the material of the fence may also affect the maximum speed that the ball can reach.