8.8 calculate the propellant mass required to launch a 2000-kg spacecraft from a 180-km-altitude circular earth orbit on a hohmann transfer trajectory to the orbit of saturn. calculate the time required for the mission and compare it with that of cassini. assume the propulsion system has a specific impulse of 300 s. {ans.: 6.03 yr; 21,810 kg}

As part of your daily workout, you lie on your back and push with your feet against a platform attached to two stiff springs arranged side by side so that they are parallel to each other. when you push the platform, you compress the springs. you do an amount of work of 79.0 j when you compress the springs a distance of 0.230 m from their uncompressed length. (a) what magnitude of force must you apply to hold the platform in this position? (b)how much additional work must you do to move the platform a distance 0.230 m farther? (c) what maximum force must you apply to move the platform a distance 0.230 m farther?