# At what velocity does the skateboard shoot off?

• cody7688
In summary, Haru says that if you make the assumption that the jump is in the fore-aft direction of the skateboard, then you get the result that the skateboard shoots off at a velocity of 3 m/s. However, if you assume that the jump is relative to the ground, then the skateboard only shoots off at a velocity of 10.8 km/h.
cody7688
A person stands still on skateboard. He then jumps off at a velocity of 3 m/s. His mass is 50 kg and the skateboard has a mass of 3.5 kg. At what velocity does the skateboard shoot off?2. Is my answer correct?
If not what did I do wrong?3. m1v1=m2v2
V= 42.857 m/s

Last edited by a moderator:
cody7688 said:
A person stands still on skateboard. He then jumps off at a velocity of 3 m/s. His mass is 50 kg and the skateboard has a mass of 3.5 kg. At what velocity does the skateboard shoot off?2. Is my answer correct?
If not what did I do wrong?
3. m1v1=m2v2
V= 42.857 m/s
Unfortunately the question does not make clear whether the 3m/s is relative to the ground (as you have assumed) or relative to the skateboard.
(In fact, it is not even clear whether the jump is in the fore-aft direction of the skateboard!)

Hello Cody, welcome to PF !

I see your post was edited by a moderator; I wonder what was changed ?!

If you make the assumption Haru mentions, you end up with the result you obtained. It is worth checking if that is realistic (even if exercise composers and reallity are rather often at odds...)

3 m/s is 10.8 km/h, so modest running speed. It's difficult to give yourself that speed in a fraction of a second even when on solid ground, let alone when on a skateboard !
Assume you have 0.1 sec to push off (by then the skateboard is well under way - as we will see).
That requires an acceleration of 430 m/s2 and a force of 430 * 3.5 = 1500 N. Three times body weight !
And in 0.1 s, the board is ½ * 430 * 0.12 = 2.14 m away. More than 2 leg lengths. So even the 0.1 is too long !

Shorter legs ? 0.03 s pushing time (to get the 2.14 m down to 0.64 m) requires 5000 N, ten times body weight. No way !

(All these calculations are rough: assuming constant acceleration gives reasonable estimates, though)
--

My conclusion: the 3 m/s is wrt the board. Less sensational, I agree.
I do get reasonable numbers.
Anyone beg to differ ?

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## 1. What is the velocity of a skateboard when it shoots off?

The velocity of a skateboard when it shoots off can vary depending on factors such as the force applied, the weight of the skateboarder, and the surface being ridden on. In general, a skateboard can shoot off at speeds ranging from 5-15 miles per hour.

## 2. How does the velocity of a skateboard affect its movement?

The velocity of a skateboard directly affects its movement. The higher the velocity, the faster the skateboard will move. However, factors such as friction and air resistance can also impact the movement of the skateboard.

## 3. What is the relationship between velocity and force in skateboarding?

In skateboarding, velocity and force are directly related. The greater the force applied, the higher the velocity of the skateboard will be. This is why skateboarders often use their feet to push off the ground to increase their velocity.

## 4. Can the velocity of a skateboard be controlled?

Yes, the velocity of a skateboard can be controlled by the rider. By adjusting their body position, applying varying levels of force, and choosing different surfaces to ride on, a skateboarder can control the velocity at which their skateboard shoots off.

## 5. Is the velocity of a skateboard constant?

No, the velocity of a skateboard is not constant. As the skateboard moves, factors such as friction, air resistance, and changes in the surface can cause the velocity to fluctuate. This is why skateboarders need to constantly adjust their movements to maintain control of their skateboard's velocity.

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