physics question , I need help!?

Question

Suppose that the coefficient of friction between your feet and the floor, while wearing socks, is 0.250. Knowing this, you decide to get a running start and then slide across the floor.
Part A
If your speed is 3.00 when you start to slide, what distance will you slide before stopping?
Express your answer in meters.
1.84
Correct



Part B
Now, suppose that your young cousin sees you sliding and takes off her shoes so that she can slide as well (assume her socks have the same coefficient of friction as yours). Instead of getting a running start, she asks you to give her a push. So, you push her with a force of 125 over a distance of 1.00 . If her mass is 20.0 , what distance does she slide (i.e., how far does she move after the push ends)? Remember that the friction force is acting anytime that she is moving.
Express your answer in meters.

Answer 1

This problem is about conservation of energy, kinetic energy, work, and force of friction.

A.

Let x= distance he slid in meters

Energy at start=Kinetic Energy

KE=1/2mv^2
=1/2m(3^2)
=4.5m
This is converted to Work Energy to overcome friction, f.

Work=fx

f=uN, where N=m*9.8 Newtons, and u is given
as 0.250
f=um*9.8
=0.250*9.8m
=2.45m

Work=2.45mx

KE=Work
4.5m=2.45mx
x=4.5/2.45
=1.84meters

Note: We don't need to know his mass because it cancels out in our equation.

B.

Let x= distance she moved after the push.

Work energy as a result of the push is
125*1=125joules

Work energy in overcoming friction is fx.
f=uN
=0.250*20*9.8
=49Newtons
Work energy =49x

125=49x
x=125/49
=2.55 meters

Answer 2

Your kinetic energy when you start to slide is .5*m*v^2, where m is your mass and v is your velocity. The work (energy) done by friction is given by f*s, where f = frictional force (assumed constant) and s the sliding distance. The frictional force is f = µ*m*g, where µ is the coefficient of friction, g = acceleration of gravity (9.8m/sec^2). Equate these energies
,5*m*v^2 = µ*m*g*s and solve for s.

You have to figure the energy the cousin gets from the push. Use the same formula to find the work done by the push E = f*x. In this case, the force is the pushing force minus the friction force, as this is the force that produces the kinetic energy at the end of the push. The rest of the solution is found the same way as above, knowing the starting energy.

Answer 3

are you xi class student your answer can be find in any refresher of physics in chapter friction its very clear there. try it.