Calculating Work Done by Gravity on a Falling Skydiver

In summary, the conversation discusses a skydiver falling at terminal velocity and the calculation of work done by gravity on her. The solution involves finding the skydiver's mass using her weight and acceleration due to gravity, and then calculating the gain in kinetic energy. The final answer is 31,500W, which is found using the formula for power.
  • #1
synkk
216
0

Homework Statement


A skydiver is falling at a terminal velocity of 45 metres per second. If her weight is 700N, at what rate is gravity doing work on her?



Homework Equations


P = W / t
P = F * (d/t) = f*v
v = d/t
w = F * d



The Attempt at a Solution



Pretty confused at this question, this is all i got:

v = 45m/s

p = 45 * 700 = 31500
31500 = 700 * (d/t)

thats about it, I'm not even sure if I'm on the right track.

PS, sorry for asking such a newbie question hope someone can help, thanks...
 
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  • #2
Well gravity would be cause the work done to be entirely kinetic energy. So you just need to apply that formula.
 
  • #3
i don't see how i could apply that as i don't have the mass to find out the kinetic energy gained.
 
  • #4
synkk said:
i don't see how i could apply that as i don't have the mass to find out the kinetic energy gained.

You have her weight which is related to mass and acceleration due to gravity.
 
  • #5
uhm I'm not quite sure what you mean, i don't see how the 700N can relate to the kinetic energy.

ek = 0.5 * m * v^2

why would m = 700N? and if it does that means the gain in kinetic energy would be 708750J, where would i go from there?

sorry but i'd need more htan a sentance or two explanation as I'm trying teach myself these things, thanks anyway.
 
  • #6
synkk said:
uhm I'm not quite sure what you mean, i don't see how the 700N can relate to the kinetic energy.

700 Newtons is her weight, weight is related to mass 'm' by W = mg where g is acceleration due to gravity (on Earth this is 9.81 m/s2)

synkk said:
why would m = 700N? and if it does that means the gain in kinetic energy would be 708750J, where would i go from there?

sorry but i'd need more htan a sentance or two explanation as I'm trying teach myself these things, thanks anyway.


You will need to calculate m from the 700 N weight.

Her kinetic energy will be the work done by gravity since she is at terminal velocity.
 
  • #7
weight (force) = mass times gravity

mass = weight (force) divided by gravity

Her weight is 700N and gravity is 9.81m/s^2
 
  • #8
Okay so m = 71.4kg ( 700/9.81 )

using this the gain in kinetic energy is 72292.5J

i've taken a look at the answer and it's 31 500W, i thought i'd be figuring out the work done which is calculated in joules, now my head is going everywhere. :\
 
  • #9
synkk said:
Okay so m = 71.4kg ( 700/9.81 )

using this the gain in kinetic energy is 72292.5J

i've taken a look at the answer and it's 31 500W, i thought i'd be figuring out the work done which is calculated in joules, now my head is going everywhere. :\

Sorry sorry, I initially read the question as what is the work done by gravity.

Your initial way is correct :redface:
 
  • #10
No worries, i learned how weight is related to mass due to gravity so thanks for that.

Anyone have any ideas how to go on for this question then?
 
  • #11
synkk said:
No worries, i learned how weight is related to mass due to gravity so thanks for that.

Anyone have any ideas how to go on for this question then?

The same way you did it, using power = force*velocity and in this case the force = 700 N.
 
  • #12
Lol, i had the answer from the start, sure feel like a idiot now for not understanding the question. Thanks anyway :)
 

1. What is power and work?

Power and work are two related concepts in science and engineering. Power is the rate at which work is done, or the amount of energy that is transferred per unit time. Work, on the other hand, is the application of a force over a distance. In simpler terms, power is how quickly work is done, and work is the effort put into a task.

2. How are power and work related?

Power and work are directly related to each other through the equation: Power = Work/Time. This means that an increase in power will result in an increase in work done over a given time period. Similarly, a decrease in power will result in a decrease in work done over a given time period.

3. What are the units of power and work?

The SI unit for power is watts (W), which is defined as 1 joule per second (J/s). The SI unit for work is also joules (J), which is defined as the amount of energy required to exert a force of one newton over a distance of one meter. Other common units for power and work include horsepower (hp) and foot-pounds (ft-lb).

4. How is power and work measured?

Power can be measured using a device called a power meter, which measures the rate of energy transfer. Work can be measured using a force meter, which measures the amount of force applied, and a ruler or measuring tape, which measures the distance over which the force is applied. The work is then calculated by multiplying the force by the distance.

5. What are some real-life examples of power and work?

Power and work are present in many aspects of our daily lives. For example, when you turn on a light switch, you are using power to do work by transferring energy to light up the room. When you ride a bicycle, you are using power to do work by pedaling and transferring energy to move the bike forward. In more industrial settings, power and work are used in machines and engines to produce electricity, transport goods, and perform other tasks.

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