Experience the convenience of getting your questions answered at IDNLearn.com. Receive prompt and accurate responses to your questions from our community of knowledgeable professionals ready to assist you at any time.

20. A ball of mass [tex]0.1 \, \text{kg}[/tex] is thrown vertically upwards with an initial velocity of [tex]80 \, \text{m/s}[/tex].

(i) Calculate the potential energy halfway up.
(ii) Calculate the potential energy at its maximum height.
(iii) What is its kinetic energy as it leaves the ground?


Sagot :

Alright, let's break down the problem and solve it step-by-step.

### Given:
- Mass of the ball ([tex]\( m \)[/tex]) = 0.1 kg (converted from 0.1tg)
- Initial velocity ([tex]\( u \)[/tex]) = 80 m/s
- Acceleration due to gravity ([tex]\( g \)[/tex]) = 9.8 m/s²

### 1. Calculate the Maximum Height

The kinematic equation we will use is:
[tex]\[ v^2 = u^2 - 2gh \][/tex]
Where:
- [tex]\( v \)[/tex] = final velocity (0 m/s at maximum height)
- [tex]\( h \)[/tex] = maximum height

Rearranging for [tex]\( h \)[/tex]:
[tex]\[ h = \frac{u^2}{2g} \][/tex]

### 2. Calculate the Potential Energy at Half the Maximum Height

First, we find the maximum height [tex]\( h \)[/tex]:
[tex]\[ h = \frac{(80 \, \text{m/s})^2}{2 \times 9.8 \, \text{m/s}^2} \][/tex]
[tex]\[ h = \frac{6400}{19.6} \][/tex]
[tex]\[ h = 326.53 \, \text{m} \][/tex]

Now, the half of the maximum height [tex]\( h/2 \)[/tex] is:
[tex]\[ \frac{h}{2} = \frac{326.53 \, \text{m}}{2} \][/tex]
[tex]\[ \frac{h}{2} = 163.26 \, \text{m} \][/tex]

The potential energy at half the height is:
[tex]\[ PE_{\text{halfway}} = mgh_{\text{half}} \][/tex]
[tex]\[ PE_{\text{halfway}} = 0.1 \, \text{kg} \times 9.8 \, \text{m/s}^2 \times 163.26 \, \text{m} \][/tex]
[tex]\[ PE_{\text{halfway}} = 159.99 \, \text{J} \][/tex]
Approximately, [tex]\( 160 \, \text{J} \)[/tex].

### 3. Calculate the Potential Energy at Its Maximum Height

The potential energy at maximum height is:
[tex]\[ PE_{\text{max}} = mgh \][/tex]
[tex]\[ PE_{\text{max}} = 0.1 \, \text{kg} \times 9.8 \, \text{m/s}^2 \times 326.53 \, \text{m} \][/tex]
[tex]\[ PE_{\text{max}} = 319.99 \, \text{J} \][/tex]
Approximately, [tex]\( 320 \, \text{J} \)[/tex].

### 4. Calculate the Kinetic Energy as it Leaves the Ground

The kinetic energy as it leaves the ground is given by the formula:
[tex]\[ KE = \frac{1}{2} mv^2 \][/tex]
Substituting the given values:
[tex]\[ KE = \frac{1}{2} \times 0.1 \, \text{kg} \times (80 \, \text{m/s})^2 \][/tex]
[tex]\[ KE = 0.05 \times 6400 \][/tex]
[tex]\[ KE = 320 \, \text{J} \][/tex]

### Summary

1. Potential Energy halfway up: [tex]\( 160 \, \text{J} \)[/tex]
2. Potential Energy at maximum height: [tex]\( 320 \, \text{J} \)[/tex]
3. Kinetic Energy as it leaves the ground: [tex]\( 320 \, \text{J} \)[/tex]

These are the detailed calculations and the results for each part of the problem.