Our leprechaun, mass 70 kg, jumps off a diving board that is 10 meters above the surface of a pool erected in the end zone of stadium for this week’s game. If his downward motion is stopped 2 seconds after he enters the water, what average upward force did the water exert on our favorite imp?

What horizontal force must be applied to the cart shown in order that the masses remain stationary with respect to the cart? All surfaces, pulleys, etc., can be taken to be frictionless.

Friction and Inclined Planes

Back to the inclined planes with two blocks. This time, the coefficient of static friction between the block and the inclined plane is s.Find the range of possible values for m2 such that the system will be in static equilibrium.

Newton's Third Law:LEX III.

Actioni contrariam semper et æqualem esse reactionem: sive corporum duorum actiones in se mutuo semper esse æquales et in partes contrarias dirigi.

Old Translation:To every action there is always opposed an equal reaction: or, the mutual actions of two bodies upon each other are always equal, and directed to contrary parts. What we really mean:Forces always occur in equal and opposite pairs. If object Aexerts a force on object B, an equal but opposite force is exerted by object B on object A.

Chapter 7

Two 5kg masses are connected to a scale, and the masses are at rest. The scale reads in kg. What is the reading on the scale?

5kg 5kg

A locomotive pulls a series of wagons. Which is the correct analysis of the situation?

a)The train moves forward because the locomotive pulls forward slightly harder on the wagons than the wagons pull backward on the locomotive. b) Because action always equals reaction, the locomotive cannot pull the wagon the wagons pull backward just as hard as the locomotive pulls forward, so there is no motion. c)The locomotive gets the wagons to move by giving them a tug during which the force on the wagons is momentarily greater than the force exerted by the wagons on the locomotive. d)The locomotive’s force on the wagons is as strong as the force of the wagons on the locomotive, but the frictional force on the locomotive is forward and large while the backward frictional force on the wagons is small. e)The locomotive can pull the wagons forward only if it weighs more than the wagons.

A 60-kg housepainter stands on a 15-kg aluminum platform. The platform is attached to a rope that passes through an overhead pulley, which allows the painter to raise herself and the platform. (a) To accelerate herself and the platform at a rate of 0.8 m/s2, with what force must she pull on the rope? (b) When her speed reaches 1 m/s, she pulls in such a way that she and the platform go up at a constant speed. What force is she exerting on the rope? (Ignore the mass of the rope.)