Kinetic Energy and skateboarder

In summary, a 50-kg skateboarder used a compressed spring to gain enough speed to coast up a 1.5 m ramp. The energy in the spring was calculated to be 735J using the expression 1/2kx^2, with k=1470N/m and x=1m. The wording of the question regarding kinetic energy was unclear, but it can be assumed that it was referring to the energy given by the spring before ascending the ramp. However, there is not enough information given to calculate the exact kinetic energy due to unknown variables such as the slope of the ramp and any potential energy gained during the straight run. It is suggested that the question be rewritten to ask for the total energy given by
  • #1
raman911
130
0
A50-kg skateboarder design a creative way to gain enough speed to coast up a ramp. By compressing a stiff spring. H e finds that he can go 1.5 m up the ramp?
A) How much kinetic energy does the spring give him?
B) The energy in the spring can be calculated using the expression 1/2kx^2 where k= 1470N/m and is called the spring constant and x is the distance the spring is compressed. How much was the spring compressed in this case?

My Proof

A)
Eg= mgh
Eg=50kg*9.8N/kg*1.5m
Eg=735J
So Eg=Ek
Ek=735J
B)
735J=1/2*1470N/m*x^2
x^2=1470J/1470N/m
x=1m
Is That right or Wrong?
 
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  • #2
Looks fine to me.
 
  • #3
Dick said:
Looks fine to me.
r u 100% sure?
 
  • #4
Assuming 'distance up the ramp' means vertical distance, yes. Why aren't you sure??
 
  • #5
Dick said:
Assuming 'distance up the ramp' means vertical distance, yes. Why aren't you sure??
i am confuse in B.
 
  • #6
Confused about what? Spring potential energy=gravity potential energy.
 
  • #7
Dick said:
Confused about what? Spring potential energy=gravity potential energy.

thaxxxxx u
 
  • #8
The wording on this problem has me confused also. I guess it's 1.5m vertically up from the compressed position of the spring. So that gives him 735J of gravitational POTENTIAL energy at the top, and the spring compression must be 1 meter, as you and Dick have confirmed. But part A asks about how much KINETIC energy he has. He's got none at the top, none at the start, and some varying amount in between. Are you sure part A asks for Kinetic Energy, or is this a typo??
 
  • #9
It only makes sense if the kinetic energy referred to is his kinetic energy after using the spring and before ascending the ramp. It could have been written more clearly...
 
  • #10
Dick said:
It only makes sense if the kinetic energy referred to is his kinetic energy after using the spring and before ascending the ramp. It could have been written more clearly...
But I don't think there is enuf info given to solve it, since he will have GPE as well as KE just after using the spring, which is unknown without knowing the slope.
 
  • #11
PhanthomJay said:
But I don't think there is enuf info given to solve it, since he will have GPE as well as KE just after using the spring, which is unknown without knowing the slope.

Not if there is a straight run before hitting the ramp. In any event question A should be rewritten to ask "how much energy did the spring give him". Not "kinetic energy". Then the answer is unambiguous and not subject to nit picking.
 
  • #12
Dick said:
Not if there is a straight run before hitting the ramp. In any event question A should be rewritten to ask "how much energy did the spring give him". Not "kinetic energy". Then the answer is unambiguous and not subject to nit picking.
Yes, I wasn't envisioning the 'straight run' concept.
 
  • #13
here diagram

http://img389.imageshack.us/img389/1103/physicrs1.png
 
Last edited by a moderator:
  • #14
As perfectly envisioned by Dick.
 

1. What is kinetic energy and how does it relate to skateboarding?

Kinetic energy is the energy an object possesses due to its motion. In skateboarding, kinetic energy is generated when the skateboarder moves and performs tricks, such as ollies and kickflips. The faster the skateboarder moves, the more kinetic energy they have, which can be used to perform more advanced tricks.

2. How is kinetic energy calculated for a skateboarder?

Kinetic energy is calculated using the formula KE = 1/2 * m * v^2, where m is the mass of the skateboarder and v is their velocity. This means that a skateboarder with a greater mass and/or higher velocity will have a higher kinetic energy.

3. What safety precautions should be taken to reduce the risk of injury due to kinetic energy while skateboarding?

To reduce the risk of injury while skateboarding, it is important to wear proper safety gear such as a helmet, knee and elbow pads, and wrist guards. It is also important to practice and master basic skills before attempting more advanced tricks, and to always be aware of one's surroundings.

4. Can kinetic energy be converted into other forms of energy while skateboarding?

Yes, kinetic energy can be converted into other forms of energy while skateboarding. For example, when a skateboarder performs a trick, the kinetic energy they have built up is converted into potential energy as they reach the peak of their jump. This potential energy is then converted back into kinetic energy as they land back on the ground.

5. How does friction affect the kinetic energy of a skateboarder?

Friction is a force that opposes motion, so it will act to slow down a skateboarder and decrease their kinetic energy. This is why skateboarders often apply wax or other lubricants to their boards to reduce friction and allow them to maintain their speed and kinetic energy for longer periods of time.

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