4- Find the required time for a car to move 98 m if it starts from rest and acceleration at 40 m/s? 5- A rock of mass 5 kg falls with an acceleration of 9.8 m/s2. What is the magnitude of the force acting on the rock? 6- A car with mass 2000 kg moves with velocity 20 m/s on a friction surface. If the car takes 100 m to stop, determine the friction force.