Answer:
1 : 2 cm/km or 
One cm represents 2 km.
Explanation:
If 3 cm represents 6 km on the earth, the ratio to consider is: 3 : 6 cm/km which is the same as:
1 : 2 cm/km or 
One cm represents 2 km.
Answer:
the normal force that the wall exerts on the ball
Explanation:
As Newton's third law states:
"when an object A exerts a force on object B, then object B exerts an equal and opposite force on object A".
If we apply this law to this problem, we can identify the ball as object A, and the wall as object B. As the ball hits the wall, the ball exerts a force on the wall (toward the direction of motion of the ball), so the wall exerts an equal and opposite force on the ball (in the opposite direction). This force is the normal force of the wall, and it is responsible for pushing the ball back towards Erica.
Explanation :
Work is done when a force is applied to create a displacement on an object.
Thus, the work done depends on the two factors i.e.
(1) Applied force (F)
(2) Distance or displacement (d)
Mathematically, work done is 
It also depends on the angle between the force and the displacement.

For example,
A person carries a weight of 20 kg and lifts it on his head 1.5 m above the surface. So, the work done by him on the luggage will be:

or


So, 
Hence, the work done by him on the luggage is 294 Joules.
A > Is the correct answer :)
Answer:
For A
Displacement= 1/2*3*6= 9m
For B
Displacement= 1/2*4*4= 8m