Aconstant friction force of 25 n acts on a 65-kg skier for 15 s on level snow. what is the skier’s change in velocity

Explanation:

Newton's 2nd Law relates the net force F on an object of mass m with the acceleration a it experiments by F=ma. In our case the net force is the friction force, since it's the only one the skier is experimenting horizontally and the vertical ones cancel out since he's not moving in that direction. Our acceleration then will be:

Also, acceleration is defined by the change of velocity in a given time t, so we have:

Since we want the change in velocity, mixing both equations we conclude that:

Which for our values means:

the doppler effect is used by weather forecasters to measure 

moving clouds