# Homework Help: How far will the box slide?

1. May 27, 2015

### subopolois

1. The problem statement, all variables and given/known data
How far will a box slide if its initial velocity is 1.5 m/s, kinetic friction is 0.15 and the object is 30 kg

2. Relevant equations
a= (kinetic friction)(acceleration due to gravity) and
V(final)^2 - V(initial)^2 = 2(a)(D)

3. The attempt at a solution
a= 0.15 x 9.81 m/s^2
= -1.47 m/s^2 (negative since it is slowing down)

D= V(final)^2 - V(initial)^2 / 2a
= 0 - (1.5 m/s)^2 / 2(-1.47 m/s^2)
= -2.25 m/s^2 / -2.94 m/s^2
= 0.76 m

did i do everything right? seems to me like it should go a little further given the value of friction...

2. May 27, 2015

### Staff: Mentor

Looks good to me!

3. May 27, 2015

### Staff: Mentor

You solved it using kinematics, which is perfectly fine. What other approach might you have used?

4. May 27, 2015

### subopolois

Id say id be able to use kinetic energy to solve it, yay or nay?

5. May 27, 2015

### Staff: Mentor

Yes, you could use energy methods to solve this. Good!

(Try setting it up enough to convince yourself that you get the same equation in the end.)

6. May 28, 2015

### subopolois

ok so lets say i use energy. I have this equation
v(initial)^2 = 2(mu)(g)(delta r)

and i rearrange to find r
r= v(initial)^2 / 2(mu)(g)

I put all my numbers in and i get a different answer, 0.54 meters. what did i do wrong?

7. May 28, 2015

### Staff: Mentor

Looks good. Note that this is exactly the same equation you ended up with when you solved it using kinematics.