Physics Answers

Calculate the acceleration due to gravity at the surface of the moon. The moon’s radius is about 1.7 × 106 𝑚 and its mass is 7.4 × 1022 𝑘𝑔.

Calculate the centripetal acceleration of the earth in its orbit around the sun and the net force exerted on the earth. What exerts this force on the earth? Assume the earth’s orbit is a circle of radius 1.49 × 1011 m. 

Calculate the force of gravity on a spacecraft 12,800 𝑘𝑚 above the earth’s surface if its mass is 850 𝑘𝑔. 

The moon has a mass of 7.32 × 1022 𝑘𝑔 and a radius of 1,609.4 𝑘𝑚. Calculate the value of "𝑔" at the surface of the moon.

A radio-controlled model airplane has a momentum given by [(−0.75𝑘𝑔 ∙ 𝑚 𝑠 3 ⁄ )𝑡 2 + (3.0𝑘𝑔 ∙ 𝑚⁄𝑠)]𝑖̂+ (0.25𝑘𝑔 ∙ 𝑚 𝑠 2 ⁄ )𝑡𝑗̂. What are the 𝑥-, 𝑦-, and 𝑧-components of the net force on the airplane?

Two figure skaters, one weighing 625 𝑁 and the other 725 𝑁, push off against each other on frictionless ice. (a) If the heavier skater travels at 1.50 𝑚/𝑠, how fast will the lighter one travel? (b) How much kinetic energy is “created” during the skaters’ maneuver, and where does this energy come from? 

The expanding gases that leave the muzzle of a rifle also contribute to the recoil. A 30-caliber bullet has a mass 0.00720 𝑘𝑔 and a speed of 601 𝑚/𝑠 relative to the muzzle when fired from a rifle that has a mass of 2.80 𝑘𝑔. The loosely held rifle recoils at a speed of 1.85 𝑚/𝑠 relative to the earth. Find the momentum of the propellant gases in a coordinate system attached to the earth as they leave the muzzle of the rifle.

Ice hockey star Wayne Gretzky is skating at 13.0 𝑚/𝑠 toward a defender, who, in turn, is skating at 5.00 𝑚/𝑠 toward Gretzky, shown in Figure right. Gretzky’s weight is 756 𝑁; that of the defender is 900 𝑁. Immediately after the collision, Gretzky is moving at 1.50 𝑚/𝑠 in his original direction. Neglect external horizontal forces applied by the ice to the skaters during the collision. A) What is the velocity of the defender immediately after the collision? b) Calculate the change in the combined kinetic energy of the two players.

You are standing on a sheet of ice that covers the football stadium parking lot in Buffalo; there is negligible friction between your feet and the ice. A friend throws you a 0.400-𝑘𝑔 ball that is traveling horizontally at 10.0 𝑚/𝑠. Your mass is 70.0 𝑘𝑔. a) If you catch the ball, with what speed do you and move afterward? b) If the ball hits you and bounces off your chest, so afterward it is moving horizontally at 8.0 𝑚/𝑠 in the opposite direction, what is your speed after the collision?

A 68.5-kg astronaut is doing a repair in space on the orbiting space station. She throws a 2.25-𝑘𝑔 tool away from her at 3.20 𝑚/𝑠 relative to the space station. With what speed and in what direction will she begin to move?