If we accelerate a radioactive isotope of an element in a particle accelerator to a speed close to that of light, what would its observed rate of decay be compared to its rate of decay at rest

truck y has a greater velocity than truck x.

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