Why does air at 75% relative humidity and 30°c make your skin feel stickier than air at 75% relative humidity at 10°c

What efficiency of a car's engine when heat input is 200,000 joules and waste heat is 150,000 joules? a. 75% b. 35% c. 25% d. 85%

Which statement is true about an object that is moving in a circular motion due to centripetal force, f, when the radius of its circular motion is doubled? the new force then becomes equal to 2f the new force then becomes equal to f the new force then becomes equal to f/2 the new force then becomes equal to f2 the new force then becomes equal to 1/f

Ineed to answer this problem but i lack in knowledge, what should i study to answer this problem? i have never used derivatives in a physics problem so i'm not sure what's happening and i can't find videos explaining.