4. A 28.0 kg crate is being push across a horizontal floor with a force F = 155 N that makes an angle θ = 28.0° with the horizontal as illustrated in the figure below. Find the magnitude of the acceleration of the crate, given that the coefficient of kinetic friction between the crate and the floor is 0.13.

What forces cause (a) an automobile, (b) a propeller-driven airplane, and (c) a rowboat to move?

A student decides to move a box of books into her dormitory room by pulling on a rope attached to the box. She pulls with a force of 80.0 N at an angle of 25.0 above the horizontal. The box has a mass of 25.0 kg, and the coefficient of kinetic friction between box and floor is 0.300. (a) Find the acceleration of the box. (b) The student now starts moving the box up a 10.0 incline, keeping her 80.0 N force directed at 25.0 above the line of the incline. If the coefficient of friction is unchanged, what is the new acceleration of the box?

(a) Find the tension in each cable supporting the 6.00 102-N cat burglar in Figure P4.35. (b) Suppose the horizontal cable were reattached higher up on the wall. Would the tension in the other cables increase, decrease, or stay the same? Why? Figure P4.35

An object of mass m is dropped from the roof of a building of height h. While the object is falling, a wind blowing parallel to the face of the building exerts a constant horizontal force F on the object. (a) How long does it take the object to strike the ground? Express the time t in terms of g and h. (b) Find an expression in terms of m and F for the acceleration ax of the object in the horizontal direction (taken as the positive x-direction). (c) How far is the object displaced horizontally before hitting the ground? Answer in terms of m, g, F, and h. (d) Find the magnitude of the objects acceleration while it is falling, using the variables F, m, and g.

An object of mass m is dropped al t = 0 from the roof of a building of height h. While the object is falling, a wind blowing parallel to the face of the building exerts a constant horizontal force F on the object. (a) At what time t does the object strike the ground? Express t in terms of g and h. (b) Find an expression in terms of m and F for the acceleration ax of the object in the horizontal direction (taken as the positive x direction). (c) How far is the object displaced horizontally before hitting the ground? Answer in terms of m, g, F, and h. (d) Find the magnitude of the objects acceleration while it is falling, using the variables F, m, and g.

A horizontal force of 95.0 N is applied to a 60.0.kg crate on a rough, level surface. If the crate accelerates at 1.20 m/s2, what is the magnitude of the force of kinetic friction acting on the crate? (See Section 4.5.)

Two forces are applied to a car in an effort to move it, as shown in Figure P4.12. (a) What is the resultant vector of these two forces? (b) If the car has a mass of 3 000 kg, what acceleration does it have? Ignore friction. Figure P4.12

Calculate the normal force on a 15.0 kg block in the following circumstances: (a) The block is resting on a level surface. (b) The block is resting on a surface tilted up at a 30.0 angle with respect to the horizontal. (c) The block is resting on the floor of an elevator that is accelerating upwards at 3.00 m./s2. (d) The block is on a level surface and a force of 125 N is exerted on it at an angle of 30.0 above the horizontal. (Sec Section 1.5.)

A block of mass 3.00 kg is pushed up against a wall by a force P that makes an angle of = 50.0 with the horizontal as shown in Figure P5.34. The coefficient of static friction between the block and the wall is 0.250. (a) Determine the possible values for the magnitude of P that allow the block to remain stationary. (b) Describe what happens if P has a larger value and what happens if it is smaller. (c) Repeal parts (a) and (b), assuming the force makes an angle of = 13.0 with the horizontal. Figure P5.34