Universal Gravitation

At what distance from the Earth will a spacecraft on the way to the moon experience zero net force due to these two bodies because the Earth and moon pull with equal and opposite forces? Thanks

Gravitation problem

A hypothetical planet has a radius 2.5 times that of Earth, but has the same mass. What is the acceleration due to gravity near its surface?

Newton's Laws

If the coefficient of kinetic friction between a 12.0 kg crate and the floor is .30, what horizontal force is required to move the crate at a steady speed across the floor? What horizontal force is required if µk is zero?

help

A skier is pulled by a tow rope up a frictionless ski slope that makes an angel of 12 degree with the horizontal. The rope moves parallel to the slope with a constant speed of 1.0m/s. The force of the rope does 900J of work on the skier as the skier moves a distance of 8.0m up the incline. (a) If the rope moved with a constant speed of 2.0m/s, how much work would the force of the rope do on the skier as the skier moved a distance of 8.0 m up the incline? At what rate is the force of the rope doing work on the skier when the rope moves with a speed of (b)1.0m/s? and (c) 2.0m/s? Thanks.

physics

A 250g block is dropped onto a relaxed vertical spring that has a spring constant of k =2.5 N/m. The block becomes attached to the spring and compresses the spring 12 cm before momentarily stopping. While the spring is being compressed, what work is being done on the block by (a) the gravitational force and (b) the spring force? (c) what is the speed of teh block just befor it hits the spring? (d) if the impact speed is doubled, what is the maximal spring's compression.