A man accelerates a crate across a rough, level floor with an efficiency of 50%. Which is true? Group of answer choices

Energy is not conserved, because the efficiency is less than 100%.

Part of the man’s work goes into the kinetic energy of the crate, while the other part of his work is done against friction.

The energy gained by the crate equals the work done by the man.

The work done by the man equals the distance the crate moves multiplied by the friction.

You have been hired to design a spring-launched roller coaster thatwill carry two passengers per car. the car goes up a 10-m highhill, then descends 15m to the track's lowest point. you'vedetermined that the spring can be compressed a maximum o 2.0m andthat a loaded car will have a maximum mass of 400kg. for safetyreasons, the spring constant should be 10% larger than the minimumneeded for the car to just make it over the top. a) what spring constant (k) should you specify ? b) what is the maximum speed of a 350 kg car if the spring iscompressed the full amount.