I found the answer to my question. We can resolve the above issue by setting the viewport height to device height, this can be in 2 ways, one is myapp.gwt.xml configuration and the other is, adding these lines in our onModuleLoad()
1)xml configuration:see this:viewport height adjustment
2)code snippet::
MGWTSettings settings = MGWTSettings.getAppSetting();
ViewPort viewPort = settings.getViewPort();
viewPort.setHeightToDeviceHeight();
viewPort.setWidthToDeviceWidth();
viewPort.setUserScaleAble(false).setMinimumScale(1.0).setMinimumScale(1.0).setMaximumScale(1.0);
viewPort.setTargetDensity(DENSITY.MEDIUM);
settings.setViewPort(viewPort);
MGWT.applySettings(settings);