Find the speed of a Block going up an incline

[Lucy90]

Homework Statement

What is the speed after 5 seconds?
Given
Box1 : 400 kg
Box2: 100 kg
Initial velocity: 20 m/s
μk: .30
Angle of Incline: 25
Time: 5 seconds

Homework Equations

Force of Friction: (mg)(cos θ)(μ)
Effective Gravity: (mg)(sinθ)
F=ma
Vf = Vi + at

The Attempt at a Solution

For Force of friction I got 1066.9055
For Effective Gravity I got 1658.3540
Then I added the weight from the 100 kg block

Then I did Fnet = -1066.91-1658.35 + 981 = 500a
a = -3.49

Vf = Vi + at
Vf = 20 + (-3.49)(5)
Vf = 2.55

I'm not sure if this is correct

 

[gneill]

Hi Lucy90,

Welcome to Physics Forums.

Your numerical result looks fine, but the units are missing. Always be sure to include the units on numbers that are results (including intermediate results). It helps with checking, and markers will usually deduct points (or simply mark the answer wrong) if they are left out. It's good to get into the habit of always including them.