Answer:
-0.4D(maybe)
Explanation:
combined focal length (f)= 0.4m
D1 = 5D
Then f1= 1/D1
= 1/5 = 0.2 m
1/f=1/f1+1/f2
1/0.4=1/0.2+1/f2
f2= -5/2
D2=1/f2= -0.4D
(a) The work done by the bird to raise the snake on the branch is equal to the product between the weight of the snake and the height of the branch above the ground:

where
is the mass of the snake and
is the height of the branch with respect to the ground. Substituting numbers into the equation, we find

(b) The work the bird did to raise its own centre of mass from the ground to the branch is equal to the product between the bird's weight and the height of the branch:

where
is the mass of the bird. Substituting numbers into the equation, we find

The displacement is 2 m south
Explanation:
Distance and displacement are two different quantities:
- Distance is the total length of the path covered by an object during its motion, regardless of the direction. It is a scalar quantity
- Displacement is a vector connecting the initial position to the final position of motion of an object. The magnitude of the displacement is the distance in a straight line between the two points
For the car in this problem, the motion is:
10 m south
8 m north
Taking north as positive direction, we can describe the two parts of the motion as

m
Therefore, the final position of the car with respect to the original position is

which means 2 m south: so, the displacement of the car is 2 m south.
Learn more about distance and displacement:
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If the springs are connected together from end to end, they are arranged in series. For springs in series, the forces are additive.
Spring 1: F1 = k1(Δx1)
Spring 2: F2 = k2(Δx2)
Spring 1: F3 = k3(Δx3)
Total Force = k1(Δx1)+k2(Δx2)+k3(Δx3)
Total Force = (k1+k2+k3)(Δx,total)
The spring constants are added together and multiplied with the total length of elongation to find the total force acting on it.