YA Fnet Fnet (a) (b) Figure 5.12 (a) The net force on a lawn mower is 51 N to the right. At what rate does the lawn mower accelerate to the right? (b) The free-body diagram for this problem is shown.

A commercial airplane is coming in for a landing. Just before it hits the runway it is moving at 76 m/s. The plane has a mass of 20,000 kg. The runway is 1.6km long and, obviously, the airplane needs to be stopped before it reaches the end of the runway. How large is the braking force the airplane needs to stop safely before the end of the runway?

A rope is attached to Box A, and it is pulled on a rough surface due east with friction. The mass of Box A is 50 kg, and the tension force applied to the box is 100 N due east. If Box A is pulled by the tension force for 4.0 s, and the velocity changes from 0.1 m/s due east to 0.65 m/s due east during the time Box A is pulled, answer the following questions.  (a) What is the acceleration of Box A during the time it is pulled?  (b) What is the change in kinetic energy of Box A during the time it is pulled?  (c) What is the net work done on Box A by the tension force and the frictional force together? (d) What is the work done on Box A by the tension force alone?  (e) What is the work done on Box A by the frictional force alone?

Three objects are connected as shown in the figure.  The strings and frictionless pulleys have negligible masses.  The coefficient of kinetic friction is 0.25 and static friction is 0.30.  Block A has a mass of 3 kg and block B has a mass of 4 kg.  a) What is the maximum mass block C can have before block B will start to move?  b) If block C has a mass of 7 kg. and was 1 m above the ground, how long would it take block C to hit the ground starting from rest?