Unless otherwise stated, all objects are located near the Earth's surface, where g = 9.80 {\rm m/s^2}. A person has a choice while trying to push a crate across a horizontal pad of concrete: push it at a downward angle of 25 ∘ , or pull it at an upward angle 25 ∘. If the crate has a mass of 53.0 kg and the coefficient of kinetic friction between it and the concrete is 0.790, calculate the required force to move it across the concrete at a steady speed for both situations. Unless otherwise stated, all objects are located near the Earth's surface, where g = 9.80 m/s2.
An object (mass 2.8 kg ) slides upward on a vertical wall at constant velocity when a force F of 57 N acts on it at an angle of 60∘ to the horizontal. Determine the force of kinetic friction on the object.

There is a theory that indicates that dinosaurs became extinct when about 65 million years ago, a large asteroid hit the earth surface. dust caused by this collision blocked the sunlight reaching the earth's surface and many forms of life became extinct due to the cold. fearing this threat, how large the radius of an asteroid should you be looking for if the dangerous asteroid size is approximately the same as the one that killed the dinosaurs? available data suggests that about 18% of that asteroid's mass ended up as a dust spread evenly over earth after eventually settling out of the upper atmosphere. about 0.0180 g/cm^2 of dust, which is chemically different than the earth's rock, covered the earth's surface. typical asteroids have a density of about 1.9 g/cm^3. now that we know the size of the asteroid, how much energy was released during impact, assuming all of it was just the kinetic energy of the asteroid right before the impact?

If a refrigerator is a heat pump that follows the first law of thermodynamics, how much heat was removed from food inside of the refrigerator if it released 380j of energy to the room?

At a certain instant after jumping from the airplane a, a skydiver b is in the position shown and has reached a terminal (constant) speed vb = 52 m/s. the airplane has the same constant speed va = 52 m/s, and after a period of level flight is just beginning to follow the circular path shown of radius ρa = 2330 m. (a) determine the velocity and acceleration of the airplane relative to the skydiver. (b) determine the time rate of change of the speed vr of the airplane and the radius of curvature ρr of its path, both as observed by the nonrotating skydiver.