Achild is sitting on a stationary skateboard with a pile of rocks which she throws in one direction in order to make the skateboard travel in the opposite direction. if the rocks each have a mass of 0.40 kg and she can throw them with a speed of 14 m/s relative to the ground, determine the number of rocks she must throw per minute in order to maintain a constant average speed against a 2.1 n force of friction. (note: because this is a rate, the answer may not be a whole number.)

Ablock of mass m = 2.5 kg is attached to a spring with spring constant k = 790 n/m. it is initially at rest on an inclined plane that is at an angle of 28 degrees with respect to the horizontal, and the coefficient of kinetic friction between the block and the plane is k = 0.14. in the initial position, where the spring is compressed by a distance of a = 0.18 m, the mass is at its lowest position and the spring is compressed the maximum amount. take the initial gravitational energy of the block as zero. b) if the spring pushes the block up the incline, what distance, l, in meters will the block travel before coming to rest? the spring remains attached to both the block and the fixed wall throughout its motion.

Rohit is trying to tune an instrument

Aperson walks first at a constant speed of 4.89 m/s along a straight line from point a to point b and then back along the line from b to a at a constant speed of 2.95 m/s. what is the average speed over the entire trip?