Conservation of Energy Problem - How far does each can slide?

In a hardware store, paint cans, which weigh 46.0 N
each, are transported from storage to the back of the
paint department by placing them on a ramp that is
inclined at an angle of 24.0 deg above the horizontal. The
cans slide down the ramp at a constant speed of 3.40
m/s and then slide onto a table made of the same
material as the ramp. How far does each can slide on
the table’s horizontal surface before coming to rest?

2 Answers
Jul 7, 2016

d= 12.9821/g

Explanation:

The paint cans glide without acceleration so

mu m g cos(alpha)=m g sin(alpha)

where

m can mass
g gravity acceleration
mu kinetic friction coefficient
alpha ramp angle

from this relationship we get

mu = tan(alpha) = 0.445229

When in the horizontal table the movement has initial velocity v_0
so the can carries a kinetic energy of

1/2mv_0^2 which is lost against the friction losses

1/2mv_0^2 = mu m g d where d is the glided distance over the table until repose.

so

d = 1/2 v_0^2/(mu g) = 12.9821/g

Jul 10, 2016

1.32m, rounded to two decimal places.

Explanation:

The paint cans slide down with constant speed. This means there is no acceleration and upwards force due to friction is equal and opposite to the sin theta component of gravitational force.
![wikimedia.org](useruploads.socratic.org)
If mu is the coefficient of kinetic friction and other quantities as shown in the figure
f=mu N=mu m g costheta

=>mu m g costheta=m g sintheta
We obtain
mu = tan 24^@ = 0.44523 , rounded to five decimal places

While moving on the horizontal table the can has initial velocity u. The KE due to this speed is lost in doing work against the force of friction.

If s is the distance moved on the table before coming to rest, work done against the force of friction
=(mu m g)cdot s
(material of ramp and table being same, has same coefficient of kinetic friction.)
Equating it with the KE we obtain
(mu m g)cdot s=1/2m u^2
=> s=(1/2m u^2)/(mu m g)
=> s= u^2/(2mu g)
Inserting given, calculated quantities and taking g=9.81ms^-2 we get
s= (3.40)^2/(2xx0.44523 xx9.81)
=>s=1.32m, rounded to two decimal places.