Asked by Anonymous
                A box is given an initial leftward velocity of -20 m/s.  Friction works against that motion, causing a constant acceleration of 4 m/s2 until the box stops. Hint: would acceleration be positive or negative here to slow the box down?  
How far does the box travel before it comes to rest?
How much time does the box take to stop?
            
            
        How far does the box travel before it comes to rest?
How much time does the box take to stop?
Answers
                    Answered by
            Damon
            
    if v is - , a is +
v = Vi + a t
0 = -20 + 4 t
t = 5 seconds
x = Xi + Vi t + .5 a t^2
x = 0 - 20(5) + 2 (25)
x = -100 + 50
x = -50
    
v = Vi + a t
0 = -20 + 4 t
t = 5 seconds
x = Xi + Vi t + .5 a t^2
x = 0 - 20(5) + 2 (25)
x = -100 + 50
x = -50
                    Answered by
            Anonymous
            
    I understand how you got the time but I dont really understand how x is -50
The box can travel in a negative?
    
The box can travel in a negative?
                    Answered by
            Damon
            
    sure, it has a negative velocity (leftward)
so it ends up at negative, not positive, x
    
so it ends up at negative, not positive, x
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