I think it is D
Hope my answer help you?
Demographic Barriers, Occupation, Age, Obesity, <span>
Psychological Barriers</span>
The moons belong to the following planets in the following order:
1. Callisto ==> Jupiter
2. Deimos ==> Mars
3. Europa ==> Jupiter
4. Ganymede ==>Jupiter
5. Triton ==> Neptune
6. Titan ==> Saturn
7. Phobos ==> Mars
8. Io ==> Jupiter
Hope that helped =)
Answer: 
Explanation:
Given
Length of the race track 
the radius of curvature of the track 
time taken to run on track is 
Speed of runner is

Centripetal acceleration is

A scalar quantity is one in which there is no direction given.
30 Lbs would be the answer, since there is no indicator of direction.