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View Full Version : Physics: impulse


angel124985
Nov 26, 2010, 12:55 PM
Flip (60 kg) jumps horizontally off his 0.08m high skateboard(3 kg) and lands 0.25m away. The skateboard shoots out from under him over 12 m of gravel (friction is 0.75) and reaches a frictionless ramp.---------Does the board reach the top of the ramp? If so, at what speed?

ebaines
Dec 1, 2010, 01:15 PM
Maybe yes, maybe no. You've provided enough data to allow you to demonstrate that the skate board will make it through the gravel and reach the base of the ramp. But whether it can roll to the top of the ramp depends on how high the ramp is. The process to use here is:

1) determine the initial horizontal velocity of the skater - from knowing that he moves horizontally 0.75 m in the time it takes him to fall 0.08m.
2) Use conservation of momentum to determine the initial horizontal velocity of the skate board.
3) Calculate the resulting initial kinetic energy of the skateboard
4. Calculate how much work is done by the skate board as it goes over the gravel (Work = force x distance)
5. Subtract (4) from (3) to determine how much KE is left when the board reaches the base of the ramp.
6. Compare that kinetic energy of the board when it's at the base of the ramp to the energy needed for the skate board to make it to the top of the ramp, which is mgh. If it has more KE than that, the board makes it to the top. Otherwise it falls short.