4. A vertical wall cannot exert a normal force? True or False.

7. Calculate the force a 67.0-kg high jumper must exert on the ground to produce an upward acceleration 2.90 times the acceleration due to gravity.

Express your answer in S.I. units.

9. What is the acceleration of an object with a 4500 g mass when there is a net force of 18 N on it?

Express your answer in S.I. units.

11. A 4200 kg race car starts a race with an acceleration of 19 m/s². What is the net external force on it?

Express your answer in newtons.