Friction always acts in the same direction as motion.
in the opposite direction as motion.
at a 30 degree angle to the direction of motion.
perpendicular to the direction of motion.

Aheat engine that operates on a carnot cycle has an efficiency of 0.420 when its low-temperature reservoir is at 10 ∘c.part aby how many degrees celsius must you increase the temperature of the high-temperature reservoir to increase the efficiency to 0.600 if you continue to use the same low-temperature reservoir?