VIEWS: 39 PAGES: 28 POSTED ON: 11/25/2011
How fast is Dale Earnhart’s car moving? Pizza delivery: need Osama’s GPS coordinates A window washer on a scaffold is hoisting the scaffold up the side of a building by pulling downward on a rope, as shown here. If the magnitude of the pulling force is 540 N and the combined mass of the worker and the scaffold combination is 155 kg, how long will it take him to move up by 5 m? Can Robin Hood escape? The drawing shows Robin Hood (mass = 82 kg) about to escape from a dangerous situation. With one hand, he is gripping the rope that holds up a chandelier (mass = 220 kg). When he cuts the rope where it is tied to the floor, the chandelier will fall, and he will be pulled up toward a balcony above. Ignoring the friction between the rope and the beams over which it slides, calculate the time it takes for him to rise by 4 meters to the balcony above. A monkey clinging to one end of a rope that passes over a frictionless pulley is balanced by a mirror of exactly equal weight on the other end of the rope. Can the monkey climb up or down to escape the image? The figure shows a section of an airplane cable-car system. The maximum permissible mass of each car with occupants is 2900 kg. The cars, riding on a support cable, are pulled by a second cable attached to each pylon (support tower); assume the cables are straight. What is the difference in tension between adjacent sections of pull cable if the cars at the maximum permissible mass and are being accelerated up the 35° incline at 0.83 m/s2? A student from Physics 201 finds that her car is stuck in the sand and cannot be driven out. Unable to push it out, she ties a strong rope from the front of the car to a large tree 26 m away and directly in front of the car. She then pushes on the middle of the rope with a force of 425 N in a direction perpendicular to the length of the rope. If the midpoint of the rope is displaced by 1 m, what is the force applied to the car? Can the rope ever be perfectly horizontal? The tension at which a fishing line snaps is commonly called the line's "strength.“ Assuming a constant deceleration, what minimum strength is needed for a line that is to stop a salmon of weight 85 N in 8.8 cm if the fish is initially drifting at 2.9 m/s? The Gagarin Cosmonaut Training Center is used to train Russian cosmonauts for space missions. If the device can rotate at 36 rpm and has a radius of rotation of about 20 m, what acceleration does the trainee experience? Tarzan plans to cross a gorge by swinging in an arc from a hanging vine. If his arms are capable of exerting a force of 1100 N on the rope, what is the maximum speed he can tolerate at the lowest point of his swing? His mass is 70 kg and the vine is 4.8 m long. CAUTION - DANGEROUS CURVE AHEAD - REDUCE SPEED TO 20 MPH Johnny gauged the coefficient of friction between his tires and the road to be 0.40. Calling on his extensive knowledge of physics and his skepticism of truth in advertising, he figured that the sign was there to scare, not to protect, and that he could easily take the turn at 30 mph, a full 10 mph above the posted speed limit. The turn was a tight one, 50 meters in radius. 1. Did Johnny make it? 2. How far below the true speed limit was the posted speed limit? 3. If there were no friction, the turn would have to be banked. Find the necessary angle for this banking, in order for Johnny to complete the turn at the same maximum speed as friction allowed. The set-up A daredevil stunt involves riding a motorcycle around the vertical inside wall of a cylindrical structure. If the cylinder has a radius of 15 m and the coefficient of static friction between the motorcycle tires and the wall is 1.1, what is the minimum speed that will keep the motorcycle and the rider from sliding down the wall? Secret to success End A crate starts from rest and slides 8.15 m down a ramp. When it reaches the bottom it is traveling at a speed of 5.75 m/s. If the ramp makes an angle of 22.0° with the horizontal, what is the coefficient of friction between the crate and the ramp? Applet: Incline with friction CAUTION - DANGEROUS CURVE AHEAD - REDUCE SPEED TO 20 MPH Johnny gauged the coefficient of friction between his tires and the road to be 0.40. Calling on his extensive knowledge of physics and his skepticism of truth in advertising, he figured that the sign was there to scare, not to protect, and that he could easily take the turn at 30 mph, a full 10 mph above the posted speed limit. The turn was a tight one, 50 meters in radius. 1. Did Johnny make it? 2. How far below the true speed limit was the posted speed limit? 3. If there were no friction, the turn would have to be banked. Find the necessary angle for this banking, in order for Johnny to complete the turn at the same maximum speed as friction allowed. What angle requires the smallest tension force in overcoming static friction? A circus clown weighing 890 N pulls vertically downward on a rope that passes around three pulleys and is tied around his feet. If the coefficient of static friction between the clown's feet and the ground is 0.53, what is the minimum pulling force that the clown must exert to yank his feet out from under himself? End A fish of mass m is suspended by a string as shown. The string is fastened securely at point C but will pull loose from the wall at A when the string tension exceeds 19 N. What is the maximum mass of the fish that can be supported by the string? Suppose that the coefficient of static friction ms between the rider's clothing and the canvas is 0.40 and that the cylinder's radius R is 2.1 m. What minimum speed v must the cylinder and rider have if the rider is not to fall when the floor drops? Suppose two horses pull horizontally, each with a force F, on ropes attached to a tree stump. If the angle between the two ropes is 110°, what is the resultant force? A crate starts from rest and slides 8.15 m down a ramp. When it reaches the bottom it is traveling at a speed of 5.75 m/s. If the ramp makes an angle of 22.0° with the horizontal, what is the coefficient of friction between the crate and the ramp? A 6-kg monkey climbs up a massless rope that runs over a frictionless tree limb and back down to a 23-kg package on the ground. How long will it take the monkey to reach the branch 4 m above the ground if it is able to just barely lift the package off the ground?