1. A 63.0-kg sprinter starts a race with an acceleration of 4.20 m/s2 . What is the net external force on him?

3. A cleaner pushes a 4.50-kg laundry cart in such a way that the net external force on it is 60.0 N. Calculate the magnitude of its acceleration.

4. Since astronauts in orbit are apparently weightless, a clever method of measuring their masses is needed to monitor their mass gains or losses to adjust diets. One way to do ths is to exert a known force on an astronaut and measure the acceleration produced. Suppose a net external force of 50.0 N is exerted and the astronaut's acceleration is measured to be 0.893 m/s2 . (a) Calculate her mass. (b) By exerting a force on the astronaut, the vehicle in which they orbit experiences an equal and opposite force. Discuss how this would affect the measurement of the astronaut's acceleration. Propose a method in which recoil of the vehicle is avoided.

5. the net external force on the 24-kg mower is stated to be 51 N. If the force of friction opposing the motion is 24 N, what force F (in newtons) is the person exerting on the mower? Suppose the mower is moving at 1.5 m/s when the force F is removed. How far will the mower go before stopping?

6. The rocket is decelerated at a rate of 196 m/s2 . What force is necessary to produce this deceleration? Assume that the rockets are off. The mass of the system is 2100 kg.

10. A powerful motorcycle can produce an acceleration of 3.50m/s2 while traveling at 90.0 km/h. At that speed the forces resisting motion, including friction and air resistance, total 400 N. (Air resistance is analogous to air friction. It always opposes the motion of an object.) What is the magnitude of the force the motorcycle exerts backward on the ground to produce its acceleration if the mass of the motorcycle with rider is 245 kg?

15. What net external force is exerted on a 1100-kg artillery shell fired from a battleship if the shell is accelerated at 2.4010^4m/s2 ? What is the magnitude of the force exerted on the ship by the artillery shell?

19. . (a) Calculate the tension in a vertical strand of spider web if a spider of mass 8.0010^?5kg hangs motionless on it. (b) Calculate the tension in a horizontal strand of spider web if the same spider sits motionless in the middle of it. The strand sags at an angle of 12below the horizontal. Compare this with the tension in the vertical strand (find their ratio).

20. Suppose a 60.0-kg gymnast climbs a rope. (a) What is the tension in the rope if they climb at a constant speed? (b) What is the tension in the rope if they accelerate upward at a rate of 1.50 m/s2 ?

22. Consider the baby being weighed in Figure. (a) What is the mass of the child and basket if a scale reading of 55 N is observed? (b) What is the tensionT1 in the cord attaching the baby to the scale? (c) What is the tensionT2 in the cord attaching the scale to the ceiling, if the scale has a mass of 0.500 kg? (d) Draw a sketch of the situation indicating the system of interest used to solve each part. The masses of the cords are negligible.

23. A5.0010^5-kg rocket is accelerating straight up. Its engines produce1.25010^7N of thrust, and air resistance is 4.5010^6N . What is the rocket's acceleration? Explicitly show how you follow the steps in the Problem-Solving Strategy for Newton's laws of motion.

28. Commercial airplanes are sometimes pushed out of the passenger loading area by a tractor. (a) An 1800-kg tractor exerts a force of 1.7510^4N backward on the pavement, and the system experiences forces resisting motion that total 2400 N. If the acceleration is 0.150 m/s2 , what is the mass of the airplane? (b) Calculate the force exerted by the tractor on the airplane, assuming 2200 N of the friction is experienced by the airplane. (c) Draw two sketches showing the systems of interest used to solve each part, including the free-body diagrams for each.