10.0 kg 20.0 kg FIGURE 4-43 Problem 11.\f11. 13. 15. 17. (I) What force is needed to accelerate a sled (mass = 55 kg) at 1.4 m/s2 on horizontal frictionless ice? (I) How much tension must a rope withstand if it is used to accelerate a 1210-kg car horizontally along a frictionless surface at 1.20 m/sz? (II) Superman must stop a 120-km/h train in 150 m to keep it from hitting a stalled car on the tracks. If the train's mass is 3.6 x 105 kg, how much force must he exert? Compare to the weight of the train (give as %). How much force does the train exert on Superman? (II) What average force is required to stop a 950-kg car in 8.0 5 if the car is traveling at 95 km/h? (II) A 0.140-kg baseball traveling 35.0 m/s strikes the catcher's mitt, which, in bringing the ball to rest, recoils backward 11.0 cm. What was the average force applied by the ball on the glove? (II) A 20.0-kg box rests on a table. (a) What is the weight of the box and the normal force acting on it? (b) A 10.0-kg box is placed on top of the 20.0-kg box, as shown in Fig. 443. Determine the normal force that the table exerts on the 20.0-kg box and the normal force that the 20.0-kg box exerts on the 10.0-kg box. (II) A 75-kg petty thief wants to escape from a third-story jail window. Unfortunately, a makeshift rope made of sheets tied together can support a mass of only 58 kg. How might the thief use this \"rope\" to escape? Give a quantitative answer. (II) Can cars "stop on a dime\"? Calculate the acceleration of a 1400-kg car if it can stop from 35 km/h on a dime (diameter = 1.7 cm). How many g's is this? What is the force felt by the 68-kg occupant of the car? (II) (a) What is the acceleration of two falling sky divers (total mass = 132 kg including parachute) when the upward force of air resistance is equal to one-fourth of their weight? (b) After opening the parachute, the divers descend leisurely to the ground at constant speed. What now is the force of air resistance on the sky divers and their parachute? See Fig. 444