Two cars move in the same direction, if the speed of the first car is 40km/h and the speed of the second car is 60km/h. Calculate the relative speed of the second car relative to observer: a. Standing on the ground
b. Passenger in the first car

Car batteries are often rated in amp-hours. this rating indicates the quantity of charge that can pass through the battery before the battery's chemical energy must be restored by the car's generator or some other source. the amp-hour unit is convenient for simple calculations. for example, a 60-amp-hour battery can supply a current of 1.0 a for 60 h (or 60 a for 1.0 h) before going dead. find the energy stored in the following. (a) a 58 a-h, 10 v car battery(b) a 1.3 a-h, 1.7 v flashlight battery