The speed of a car which has a constant acceleration of -2m/s2 decreases from 50km/h to 30km/h. The distance travelled needed to decreases the speed of the car is:
A. 30.7m B. 160m C. 48.2m D. 142m

Vi. on another planet, a spring with constant 4.7 n/m is set up and allowed to expand verticaly freely. 8.4kg mass is placed on the spring and the spring extends 5.28m. calculate the exected extension on earth.