A cat usually lands on its feet regardless of the position from which it is dropped. A slow-motion film of a cat falling shows that the upper half of its body twists in one direction while the lower half twists in the opposite direction. Why does this type of rotation occur?
In most situations, frictional forces tend to reduce the kinetic energy of an object. However, frictional forces can sometimes increase an object's kinetic energy. Describe a few situations in which friction causes an increase in kinetic energy.
The driver of a car slams on her brakes to avoid colliding with a deer crossing the highway. What happens to the car's kinetic energy as it comes to rest?
The feet of a standing person of mass m exert a force equal to mg on the floor, and the floor exerts an equal and opposite force upwards on the feet, which we call the normal force. During the extension phase of a vertical jump, the feet exert a force on the floor that is grea...
physics - runner
While running, a person dissipates about 0.60 J of mechanical energy per step per kilogram of body mass. If a 60 kg person develops a power of 78 W during a race, how fast is the person running? (Assume a running step is 1.5 m long.)
physics - leg cast
The leg and cast in the figure below weigh 280 N, with the center of mass as indicated by the blue arrow in the diagram. The counterbalance w1 weighs 105 N. Determine the weight w2 and the angle α needed so that no force is exerted on the hip joint by the leg plus cast.
A soccer player kicks a rock horizontally off a 41.7 m high cliff into a pool of water. If the player hears the sound of the splash 3.08 s later, what was the initial speed given to the rock? Assume the speed of sound in air to be 343 m/s.
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