A sled traveling at a speed of #3.0# #ms^-1# slows to a stop #4.0# #m# from the point where its passenger rolled off. What is the magnitude of the horizontal net force that slows the #110# #N# sled?

1 Answer
Feb 17, 2016

First step is to find the acceleration (deceleration) of the sled, which turns out to be #-9/8# #ms^-2#.

Then we can use Newton's Second Law to find #F=ma=110/9.8*-9/8=-12.63# #N#

Explanation:

To find the acceleration of the sled, we use:

#v^2=u^2+2ad#

Rearranging:

#a=(v^2-u^2)/(2d)=(0^2-3^2)/(2*4)=-9/8# #ms^-2#

The minus sign just means the acceleration is in the opposite direction to the velocity: the sled is slowing down.

We want to use Newton's Second Law to find the force:

#F=ma#

We're not given the mass of the sled, but we are told its weight is #110# #N#. We know the weight force is given by #F=mg#, so we can rearrange to find:

#m=F/g=110/9.8# #kg#

So:

#F=ma=110/9.8*-9/8=-12.63# #N#

Again, the minus sign just means the force is acting in the opposite direction to the sled's initial motion.