When the velocity increases, then the acceleration will be positive and when the velocity decrease then the acceleration will be negative.
During the first hour, the velocity was 70 mph and during the seconds hour the velocity was 60 mph. Hence, the velocity decrease in the seconds hour. So, the acceleration will be negative during the second hour.
Now, during the third hour the velocity increases as it is 80 mph. Hence, the acceleration will be positive during the third hour.
Answer:
The value is 
Explanation:
From the question we are told that
The mass of the object is 
The unstressed length of the string is 
The length of the spring when it is at equilibrium is 
The initial speed (maximum speed)of the spring when given a downward blow 
Generally the maximum speed of the spring is mathematically represented as

Here A is maximum height above the floor (i.e the maximum amplitude)
and
is the angular frequency which is mathematically represented as

So

=> 
Gnerally the length of the compression(Here an assumption that the spring was compressed to the ground by the hammer is made) by the hammer is mathematically represented as

=> 
=> 
Generally at equilibrium position the net force acting on the spring is

=> 
=> 
So

=> 
Answer:
No, it is not attracted.
Explanation:
If any sphere is electrically neutral it is not attracted. The materials which are attracted by magnet are called magnetic material whereas which are not attracted are called non magnetic material. Sphere made up of non magnetic materials such as glass, wood, paper will not attracted weather is kept near north pole or near south pole.
Answer:
Advantages: In small quantities they help your body produce vitamin D.
Disadvantages: They can cause sunburn or even skin cancer if used in large quantities.
Explanation: