Josh and Taylor, standing face-to-face on frictionless ice, push off each other, causing each to slide backward. Josh is much bigger than Taylor. After the push, which of the two is moving faster?

Two teams are engaged in a tug-of-war. According to Newton's third law, the red team pulls on the blue team with the same magnitude of the force that the blue team pulls on the red team. How, then, can one team win?

A person sits on a sloped hillside. Is it ever possible to have the static friction force on this person point down the hill? Explain.

A car is skidding to a stop on a level stretch of road. Identify all the action/reaction pairs of forces between the car and the road surface. Then draw a free-body diagram for the car.

A group of students is making model cars that will be propelled by model rocket engines. These engines provide a nearly constant thrust force. The cars are light-most of the weight comes from the rocket engine-and friction and drag are very small. As the engine fires, it uses fuel, so it is much lighter at the end of the run than at the start. A student ignites the engine in a car, and the car accelerates. As the fuel burns and the car continues to speed up, the magnitude of the acceleration will A. Increase. B. Stay the same. C. Decrease.

A jet plane is speeding down the runway during takeoff. Air resistance is not negligible. Identify the forces on the jet.

In an attempt to tighten the loosened steel head of a hammer, a carpenter holds the hammer vertically, raises it up, and then brings it down rapidly, hitting the bottom end of the wood handle on a two-by-four board. Explain how this tightens the head back onto the handle.

Two persons on ice skates stand face to face and then push each other away Their masses are 60 and $90 \mathrm{~kg}$. Find the ratio of their speeds immediately afterward. Which person has the higher speed?

Internal injuries in vehicular accidents may be due to what is called the "third collision." The first collision is the vehicle hitting the external object. The second collision is the person hitting something on the inside of the car, such as the dashboard or windshield. This may cause external lacerations. The third collision, possibly the most damaging to the body, is when organs, such as the heart or brain, hit the ribcage, skull, or other confines of the body, bruising the tissues on the leading edge and tearing the organ from its supporting structures on the trailing edge. a. Why is there a third collision? In other words, why are the organs still moving after the second collision? b. If the vehicle was traveling at 60 mph before the first collision, would the organs be traveling faster than, equal to, or slower than 60 mph just before the third collision?

A person gives a box a shove so that it slides up a ramp, then reverses its motion and slides down. The direction of the force of friction is A. Always down the ramp. B. Up the ramp and then down the ramp. C. Always down the ramp. D. Down the ramp and then up the ramp.

A football player at practice pushes a 60 kg blocking sled across the field at a constant speed. The coefficient of kinetic friction between the grass and the sled is 0.30. How much force must he apply to the sled? A. 18 N B. 60 N C. 180 N D. 600 N

A Jeep is stuck in the mud. The driver has a winch that can pull on its cable with a force of $40,000 \mathrm{~N}$. The driver loops the cable through a pulley attached to a tree, then attaches the end of the cable to his Jeep, What is the maximum force that can be exerted on the Jeep by this cable arrangement?

If you know all of the forces acting on a moving object, can you tell in which direction the object is moving? If the answer is Yes, explain how. If the answer is No, give an example.

You're pushing horizontally on a large crate, but it won't budge. According to Newton's third law, the crate pushes back on you with the same magnitude of the force that you exert on it. Suddenly the crate breaks free and you can now push it along the floor. Now is the force exerted on you by the crate greater than, equal to, or less than the force that you are exerting on the crate? Explain.