What is the magnitude of the average force?

[JeSs_W]

Homework Statement

An athlete on a sled is moving with a speed of 3m/s across a pond with ice. If the total mass of the sled-athlete system is 95 kg, what magnitude of force is required to bring the sled to rest in 15 seconds?

Homework Equations

Force acting = change in momentum/time that takes for change to happen

The Attempt at a Solution

F = (95kg)/(3-0sec/15-0sec) = 19 N

 

[TheMercury79]

The Attempt at a Solution

F = (95kg)/(3-0sec/15-0sec)[/B] = 19 N

This actually equals 475 kg, which is meaningless here since you have used the formula and units for impulse incorrectly.
But 19 N•s or 19 kgm/s would be a reasonable answer so you're on the right track. You have the correct expression for
force vs. momentum in the "relevant equations" section, but you have not used it right when inserting values.

 

[haruspex]

F = (95kg)/(3-0sec/15-0sec) = 19 N

Judging from your final value, what you actually did was F = (95kg)*(3-0m/sec/15-0sec) , which is correct.