A researcher posts a newspaper advertisement offering $20 in exchange for participation in a short study. The researcher accepts the first five people who respond to the advertisement. Which of the following statements is true about the sample? (5 points) It is not a valid sample because it is only a short study. It is a valid sample because money was offered to participants. It is a valid sample because the first five people were selected to participate. It is not a valid sample because it is not a random sample of the population.

Aspacecraft can attain a stable orbit 300 kilometers above earth if it reaches a velocity of 7.7 kilometers per second. the formula for a rocket's maximum velocity v in kilometers per second is vequalsminus0.0098tplusc ln upper r, where t is the firing time in seconds, c is the velocity of the exhaust in kilometers per second, and r is the ratio of the mass of the rocket filled with fuel to the mass of the rocket without fuel. find the velocity of a spacecraft whose booster rocket has a mass ratio of 20, an exhaust velocity of 2.1 km/s, and a firing time of 15 s. can the spacecraft achieve a stable orbit 300 km above earth?