  In this work, we investigate a linear differential equation involving
Caputo-Fabrizio fractional derivative of order $1<\beta\leq 2$. Under some
assumptions the considered equation is reduced to an integer order differential
equation and solutions for different cases are obtained in explicit forms. We
also prove a uniqueness of a solution of an initial value problem with a
nonlinear differential equation containing the Caputo-Fabrizio derivative.
Application of our result to the mass-spring-damper motion is also presented.
