If mechanical energy is conserved, then a pendulum that has a potential energy of 20 j at its highest point and 0.5 j at its lowest point has as its kinetic energy at its lowest point.

20 j
0.5 j
19.5 j
20.5 j

the answer is b ) square root of 5

see the picture for the vector

the magnitude of the vector by pythagorean theorem

r = √( (-10)^2 + (3)^2 ) = √109

magnitude = √109 units

the direction angle between vector and x-axis is

tan^(-1)(3/10) = 16.699

so the direction is approximately 16.7 degrees north of west