A radioactive sample has an activity R. For which of the following changes would the activity remain unchanged?
a. The number of radioactive nuclei in the sample is doubled.
b. The half-life of the radioactive nuclei is doubled.
c. The decay constant is doubled.
d. A time period equal to two half-lives is allowed to elapse.
e. All of the above changes result in a change in the activity.
e
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A design project requires a TiNi wire to be shaped like the letter S at an operating temperature of 100°C (212°F). The selected TiNi atom arrangement starts to distort at a temperature of 90°C (194°F) and the distortion is finished at a temperature of 60°C (140°F). The wire was drawn straight at a temperature of 500°C (932°F), and the wire supplied is straight. The wire is easily bent into the required S shape at room temperature. What will be the shape of the wire at the operating temperature of 100°C (212°F)?
(a) S shaped (b) C shaped (c) Straight (d) The shape is impossible to know.
When a car goes around a circular curve on a level road without slipping,
A. no frictional force is needed because the car simply follows the road. B. the frictional force of the road on the car increases when the car's speed decreases. C. the frictional force of the road on the car increases when the car's speed increases. D. the frictional force of the road on the car increases when the car moves to the outside of the curve. E. there is no net frictional force because the road and the car exert equal and opposite forces on each other.
If an irregularly shaped object (such as a wrench) is dropped from rest in a classroom and feels no air resistance, it will
A) accelerate but will not spin. B) accelerate and turn until its center of gravity reaches its lowest point. C) accelerate and turn about its center of gravity with uniform angular speed. D) accelerate and turn about its center of gravity with uniform angular acceleration. E) accelerate and spin until its center of gravity reaches its highest point.
The work performed by a heat engine
A. equals the heat energy exhausted from the engine. B. equals the heat energy entering the engine. C. equals the net heat flow into the engine. D. equals the change in the internal energy of the engine.