A new stochastic collision model for molecular dynamics (MD) simulations at constant temperature is presented. It is based on impulsive collisions between system particles and heat bath particles of finite masses. With the algorithm one can switch between Langevin-type and Andersen-type dynamics by changing only one control parameter. The method is implemented in the simple Verlet scheme for the numerical calculation of the Newtonian equations of motion. The case of an ensemble of noninteracting particles subjected to the heat bath is considered. Analytical expressions for stationary probability densities, autocorrelation functions, and diffusion coefficients are derived. The predicitions agree excellently with the results of MD simulations.