What are the two forces involved when a machine is used?
-friction and density
-potential and kinetic
-input and output
-gravity and friction

Ahonda civic travels in a straight line along a road. its distance x from a stop sign is given as a function of time t by the equation x(t)= î± t2â î² t3, where î± = 1.53 m/s2 and î² = 5.50ã10â2 m/s3 .

Henry, whose mass is 95 kg, stands on a bathroom scale in an elevator. the scale reads 830 n for the first 2.4 s after the elevator starts moving, then 930 n for the next 2.4 s. part a what is the elevator's speed 4.8 s after starting? express your answer with the appropriate units.

In a hydrogen molecule there are a total of four charges, 2 protons in the two nuclei, and 2 electrons. how many unique charge-pairs are there (without double counting)?