On Friday, the government will offer crucial evidence when it reports on second-quarter economic growth. This will be the first in a series of indicators in the coming weeks that could help answer whether the economy has achieved cruising speed, in particular whether the private sector is growing fast enough to put unemployed Americans back to work. Forecasters are expecting that gross domestic product rose at a rate of 2 to 2.5 percent rate in the April-through-June quarter, which would be too slow to drive down the jobless rate.