Answer:
0.68 s
Explanation:
We are given that 
Initial velocity of box=
Final velocity of box=v=11.5 m/s
Distance=d=8.5 m
We have to find the time taken by box to slow by this amount.
We know that 

Substitute the values 




We know that 
Acceleration=
Substitute the values 



Hence, the time taken by box to slow by this amount=0.68 s
 
        
             
        
        
        
We want to calculate the distance covered by the drag racer. Recall, the formula for calculating distance is expressed as
Distance = speed x time
From the information given, 
speed = 320 m/s
time = 4.5 s
By substituting these values into the formula, we have
Distance = 320 m/s x 4.5s
s cancels out. We are left with m. Thus, 
Distance = 1440m
 
        
             
        
        
        
If the boat is i travling at 10 m/s and the river is 8.0 m/s the boats speed is 18.0 m/s
        
                    
             
        
        
        
Answer:
60 cm 
Explanation:
We are given;
- Focal length of a concave mirror as  30.0 cm 
- Object distance is 15.0 cm 
We are required to determine the radius of curvature.
We need to know that the radius of a curvature is the radius of a circle from which the curved mirror is part.
We also need to know that the radius of curvature is twice the focal length of a curved mirror.
Therefore;
Radius of curvature = 2 × Focal length
Therefore;
Radius of curvature = 2 × 30 cm
                                  = 60 cm