NEW YORK (TheStreet) -- Should you be investing in airlines now? That's what one viewer wanted to know in his tweet to Jim Cramer Tuesday at the New York Stock Exchange.

Cramer said he is still concerned about increased capacity in the airline sector. He noted that at the end of July "we're going to get numbers" from the airlines that he expects will prompt big estimate cuts. So for investors who want to be involved in the airlines, Cramer recommends waiting until then, which will present a better entry point.

As for another viewer's question about how much more pain investors in coal companyPeabody Energy (BTU) - Get Report can expect to endure, Cramer responded, "A lot." He said when the Rockies Express Pipeline, otherwise known as the REX pipeline, opens, it will be a nail in the coffin for all coal plants.

The nearly 1,700-mile long Rockies pipeline will transport Rocky Mountain gas to the Midwest and so there's "no hope for coal in this country" because coal plants will be closed and "everyone will turn to natural gas," Cramer said.

Asked about semiconductor company Micron Technology (MU) - Get Report, Cramer said he's been negative on the stock for the past two quarters and sees no reason to get positive on now.

On fitness product-maker Fitbit (FIT) - Get Report, public only a little less than two weeks, Cramer said many people are misinterpreting what Fitbit is really about. He says the company is really focused on wellness, especially for women, which he believes is a much bigger market than a lot of the bears out there think. That's why he still believes the stock can go higher.

At the time of publication, Jim Cramer's charitable trust Action Alerts PLUS held no positions in stocks mentioned.