Re: [Phys-l] block sliding on a skateboard

[Bernard Cleyet <bernardcleyet@redshift.com>]

On 2012, Feb 03, , at 15:58, LaMontagne, Bob wrote:

> Here is a simple problem I proposed to my general physics students that has generated a lot of discussion by them despite the problem's simplicity. I will throw it out here for your amusement.
>
> Lock the wheels of a long skateboard so it won't move. Now take a 1 kg mass and drop it from a short distance onto the skateboard with a horizontal speed of 2 m/s. The mass slides along the surface of the board and stops after a half meter.
>
> Now unlock the wheels and repeat the experiment. How far does the mass now slide relative to the surface of the skateboard before it stops sliding? Take the mass of the skateboard to be 10 kg. How far does it slide relative to the ground?
>
> Bob at PC


I must be stupid, why would anyone think it'l slide?** -- the coefficient of friction mass--skate board is much greater than that of the skateboard--sidewalk.

Assuming friction constant it's 4N (mass skateboard) and the coefficient is ~ 0.4

bc worried


** unless the board is on an incline or gravel