Let me try to work it out.Klaas van Aarsen said:The work done by an average resistance force $F_{friction}$ is $W_{friction}=F_{friction}\cdot \Delta h$.
Conservation of energy means that $GPE+KE$ just before the parachute opens must be equal to $GPE+KE+W_{friction}$ at the ground.
Can we find those $GPE$'s and $KE$'s?
Before parachute opensKlaas van Aarsen said:The work done by an average resistance force $F_{friction}$ is $W_{friction}=F_{friction}\cdot \Delta h$.
Conservation of energy means that $GPE+KE$ just before the parachute opens must be equal to $GPE+KE+W_{friction}$ at the ground.
Can we find those $GPE$'s and $KE$'s?
I apologize but iam not able to get the ans. Pls helpKlaas van Aarsen said:Let's do this a bit more systematically and put it in a table:
\begin{array}{|c|c|c|c|c|c|}
\hline
&h&GPE&KE&\text{Dissipated energy}&\text{Total energy} \\
\hline
\text{Initial} & 3000 & mg\cdot 3000 & 0 & 0 & mg\cdot 3000 \\
\text{Parachute opens} & 2000 & mg\cdot 2000 & mg\cdot 1000 & 0 & mg\cdot 3000 \\
\text{Ground} & 0 & 0 & \frac 12m\cdot 5^2 & F_{friction}\cdot 2000 & \frac 12m\cdot 5^2 + F_{friction}\cdot 2000 \\
\hline
\end{array}
The $\text{Total energy}$ must be the same at all times.
Can we find $F_{friction}$ from that?
I calculated using v^2= u^2+2asKlaas van Aarsen said:Let's do this a bit more systematically and put it in a table:
\begin{array}{|c|c|c|c|c|c|}
\hline
&h&GPE&KE&\text{Dissipated energy}&\text{Total energy} \\
\hline
\text{Initial} & 3000 & mg\cdot 3000 & 0 & 0 & mg\cdot 3000 \\
\text{Parachute opens} & 2000 & mg\cdot 2000 & mg\cdot 1000 & 0 & mg\cdot 3000 \\
\text{Ground} & 0 & 0 & \frac 12m\cdot 5^2 & F_{friction}\cdot 2000 & \frac 12m\cdot 5^2 + F_{friction}\cdot 2000 \\
\hline
\end{array}
The $\text{Total energy}$ must be the same at all times.
Can we find $F_{friction}$ from that?
Pls help me to calculate with the method you have used. PlsKlaas van Aarsen said:Let's do this a bit more systematically and put it in a table:
\begin{array}{|c|c|c|c|c|c|}
\hline
&h&GPE&KE&\text{Dissipated energy}&\text{Total energy} \\
\hline
\text{Initial} & 3000 & mg\cdot 3000 & 0 & 0 & mg\cdot 3000 \\
\text{Parachute opens} & 2000 & mg\cdot 2000 & mg\cdot 1000 & 0 & mg\cdot 3000 \\
\text{Ground} & 0 & 0 & \frac 12m\cdot 5^2 & F_{friction}\cdot 2000 & \frac 12m\cdot 5^2 + F_{friction}\cdot 2000 \\
\hline
\end{array}
The $\text{Total energy}$ must be the same at all times.
Can we find $F_{friction}$ from that?
Thank you so much!Klaas van Aarsen said:Please do not bump. That is, please do not post a useless post just to attract attention.
We don't need to calculate the speed.
The energy at the beginning is $mg\cdot 3000$.
We have the same total energy when the parachute opens.
And at the ground the total energy is $\frac 12m\cdot 5^2 + F_{friction}\cdot 2000$.
At each point in time the total energy must be the same. So:
$$mg\cdot 3000 = \frac 12m\cdot 5^2 + F_{friction}\cdot 2000 \implies F_{friction}=\frac{mg\cdot 3000 - \frac 12m\cdot 5^2}{2000}$$
We can now fill in $m=80\text{ kg}$ and $g=10\text{ m/s}^2$.
The work energy principle states that the work done on an object is equal to the change in its kinetic energy. In other words, the net work done on an object will result in a change in its speed or direction of motion.
Work and energy are closely related concepts. Work is the transfer of energy from one system to another, and energy is the ability to do work. When work is done on an object, its energy changes.
The formula for calculating work is W = F * d * cosθ, where W is work, F is the applied force, d is the displacement, and θ is the angle between the force and displacement vectors.
Power is the rate at which work is done or energy is transferred. It is calculated by dividing the work done by the time taken to do it. The unit of power is watts (W), which is equal to one joule per second (J/s).
The work energy principle can be applied in various real-world situations, such as calculating the energy needed to lift an object to a certain height, determining the power output of a car engine, or understanding the motion of a pendulum. It is a fundamental concept in physics and is used in many fields, including engineering, mechanics, and thermodynamics.