6 Forces 1. The propellers of a small airplane produce a forward thrust of 6.2 ! 104 N on the plane which has a mass of 2.8 ! 104 kg. What is the plane’s forward acceleration? 2. If the plane in Problem 1 is flying horizontally, what is the lift (upward force of air) on the plane? 3. A girl in a canoe uses a paddle to push the canoe at rest from a dock giving it a speed of 0.30 m/s. If the paddle is in contact with the dock for 0.75 seconds, what is the average force on the canoe? (The mass of the canoe is 27 kg and that of the girl is 52 kg.) 4. A student attaches a spring scale to a 2.30-kg book and then releases the book. If the student maintains a scale reading of 25.0 N, what is the magnitude and direction of the book’s acceleration? (Assume upward is the positive direction.) 5. If the student in problem 4 maintains a scale reading of 22.0 N, what will be the displacement of the book in 1.0 s? Copyright © by Glencoe/McGraw-Hill 6. Two laboratory masses are tied to opposite ends of a weightless string, which passes over a frictionless pulley as shown below. c. A student decides to demonstrate this problem. After setting up the equipment, she accurately measures the time it takes the 0.350-kg mass to reach the floor as 0.92 s. If she attributes the cause of the difference in times to the frictional force on the pulley, what is the size of this force? 7. A horse is pulling two loaded sleds across the snow. The first sled, which has a mass of 250 kg, is attached to the horse by a harness that can withstand a maximum tension of 4500 N. The second sled, which has a mass of 150 kg, is attached to the first sled by a rope that can withstand a maximum tension of 450 N. a. What is the acceleration of the sleds just before the rope snaps? b. What is the tension in the harness just before the rope snaps? 8. A pendulum with a length of 1.00 m is in a rocket that is far removed from any gravitational effects. If the rocket is accelerating as shown below, what is the period of the pendulum? Frictionless pulley v 0.350 kg 0.250 kg a " 3.2 m/s2 0.500 m a. If the masses are released from rest, what is the acceleration of the 0.250-kg mass? b. After the masses are released, how long will it take the 0.350 kg mass to strike the floor? Physics: Principles and Problems Supplemental Problems • Chapter 6 9 6 Forces 9. A 65.0-kg passenger in a car is securely fastened in a safety belt as shown below. x m " 65.0 kg Safety belt Calculate the magnitude and determine the direction of the horizontal force that the safety belt and seat exert on the passenger for each of the following conditions. (Assume the car is moving only horizontally.) 10. In Problem 9, the car is traveling at 20.0 m/s and the driver suddenly slows down the car at a rate of 5.00 m/s2. a. What is the magnitude and direction of the force that the passenger exerts on the safety belt and seat? b. After slowing down, the driver accelerates the car forward at a rate of 1.50 m/s2. What is the magnitude and direction of the force that the passenger exerts on the safety belt and seat? a. v0 " #20.0 m/s, a " 0 m/s2 b. v0 " #20.0 m/s, a " #1.50 m/s2 c. v0 " 10.0 m/s, a " $3.00 m/s2 d. v0 " $3.0 m/s, a " $1.20 m/s2 e. v0 " $10.0 m/s, a " #2.3 m/s2 Copyright © by Glencoe/McGraw-Hill 10 Supplemental Problems • Chapter 6 Physics: Principles and Problems