Explanation:
average speed = total distance travelled / total time travelled
time to travel the first 6km: 6 / 50 = 3/25 (h)
time to travel the next 6km: 6 / 90 = 1/15 (h)
[I think there's problem in the question 'cause 900km/h sounds impossible for normal person to travel in normal condition]
The total time: 3/25 + 1/15 = 14/75 (h)
Average speed over the 12 km drive will be:

T= 3.34
Vi= 0
A= 9.81
D= ?
d=Vit+1/2at^2
d= 1/2(9.81)(3.34)2
d= 54.7 or 55 meters tall
From that list, only the frequency makes the difference.
Einstein won his only Nobel Prize for his explanation of this effect.
Answer:
0.010 m
Explanation:
So the equation for a pendulum period is:
where L is the length of the pendulum. In this case I'll use the approximation of pi as 3.14, and g=9.8 m\s. So given that it oscillates once every 1.99 seconds. you have the equation:

Evaluate the multiplication in front

Divide both sides by 6.28

Square both sides

Multiply both sides by m/s^2 (the s^2 will cancel out)
Now now let's find the length when it's two seconds

Divide both sides by 6.28

Square both sides

Multiply both sides by 9.8 m/s^2 (s^2 will cancel out)

So to find the difference you simply subtract
0.984 - 0.994 = 0.010 m