Answer
When you jump and your feet leave the floor, your horizontal motion has not changed; you have the same 1000 km/hr horizontal speed that the Earth beneath you has.
Work Step by Step
From your own viewpoint, you simply move straight up and down.
Please see page 34 for a discussion of this exact situation, and refer to Figure 2.19 and the text for a similar example of a coin tossed in an airplane.
