Exam 4: Dynamics: Newtons Laws of Motion

A 55-kg box rests on a horizontal surface. The coefficient of static friction between the box and the surface is 0.30. A horizontal 140-N force is applied to the box. What is the friction force on the box?

Two packages are connected by a very light string that goes over an ideal pulley as shown in the figure. Package A has a mass of 3.0 kg and can slide along a rough plane inclined at above the horizontal. The string acts on package A parallel to the surface of the plane. The coefficient of static friction between package A and the plane is 0.40 . What minimum mass should package B have in order to start package A sliding up the ramp?

A block is on a frictionless table, on earth. The block accelerates at 5.3 m/s² when a 10 N horizontal force is applied to it. The block and table are set up on the Moon where the acceleration due to Gravity is 1.62 m/s². A horizontal force of 5 N is now applied to the block when it is on the Moon. The acceleration imparted to the block by this force is closest to

An object slides on a level floor. It slows and comes to a stop with a constant acceleration of magnitude 2.4 m/s². What is the coefficient of kinetic friction between the object and the floor?

You push horizontally on a 120-N box that is initially resting on a horizontal table. The coefficient of static friction between the box and the table is 0.75, and the coefficient of kinetic friction is 0.40. Find the friction force on the box if the push is equal to (a) 84 N; (b) 94 N.

A 958-N rocket is coming in for a vertical landing. It starts with a downward speed of 25 m/s and must reduce its speed to 0 m/s in 8.0 s for the final landing. (a) During this landing maneuver, what must be the thrust due to the rocket's engines? (b) What must be the direction of the engine thrust force?

As shown in the figure, two blocks are connected by a very light string, and the upper block is pulled upward by a different string. The masses of the upper and lower blocks are 300 g and 240 g, respectively. The string between the blocks will break if its tension exceeds 3.6 N, and the string that pulls the combination upward will break if its tension exceeds 7.8 N. (a) What is the largest upward acceleration that the blocks can be given without either string breaking? (b) If the upward acceleration is slightly higher than this, which string breaks, the upper one or the lower one?

A flatbed truck is carrying an 800-kg load of timber that is not tied down. The maximum friction force between the truck bed and the load is 2400 N. What is the greatest acceleration that the truck can have without losing its load?

A 20-ton truck collides with a 1500-lb car. Which of the following statements must be true?

The acceleration due to gravity is lower on the Moon than on Earth. Which one of the following statements is true about the mass and weight of an astronaut on the Moon's surface, compared to Earth?

Three objects are connected by weightless flexible strings as shown in the figure. The pulley has no appreciable mass or friction, and the string connected to the block on the horizontal bench pulls on it parallel to the bench surface. The coefficients of friction between the bench and the block on it are and You observe that this system remains at rest. (a) Find the mass of the hanging object A. (b) What is the magnitude of the friction force on the block on the bench?

A policeman investigating an accident measures the skid marks left by a car on the horizontal road. He determines that the distance between the point that the driver slammed on the brakes (thereby locking the wheels) and the point where the car came to a stop was 28.0 m. From a Reference manual he determines that the coefficient of kinetic friction between the tires and the Road under the prevailing conditions was 0.300. How fast was the car going when the driver Applied the brakes?

A bulldozer attempts to drag a log weighing 500 N along the rough horizontal ground. The cable attached to the log makes an angle of 30° above the ground. The coefficient of static friction between the log and the ground is 0.50, and the coefficient of kinetic friction is 0.35. What minimum tension is required in the cable in order for the log to begin to slide?

A box is placed on a table which rests on the floor. The box pushes on the table; the reaction force to the box's push on the table is the table's push on the floor.

During a hockey game, a puck is given an initial speed of 10 m/s. It slides 50 m on the horizontal ice before it stops due to friction. What is the coefficient of kinetic friction between the puck and The ice?

An object of weight W is in freefall close to the surface of Earth. The magnitude of the force that the object exerts on Earth is

A slanted roof rises at ° above the horizontal, and the straight-line distance from the top of the roof to the bottom edge is 4.5 m. The roof is covered with ice, so it offers no friction to objects sliding on it. A piece of ice at the top suddenly breaks loose and begins to slide down from rest. (a) How long will it take for the ice to reach the bottom edge of the roof? (b) How fast will the ice be traveling just as it reaches the bottom edge?

A 50.0-kg block is being pulled up a slope by a force of 250 N that is parallel to the slope. The coefficient of kinetic friction between the block and the slope is 0.200. What is the acceleration of The block?

Two objects of unequal masses, M and m(M > m) , are connected by a very light cord passing over an ideal pulley of negligible mass. When released, the system accelerates, and friction is negligible. Which one of the following free-body diagrams most realistically represents the forces acting on the two objects in the moving system?

A car of mass 1100 kg that is traveling at 27 m/s starts to slow down and comes to a complete stop in 578 m. What is the magnitude of the average braking force acting on the car?