Which device is similar to a sandwich that has layers of semiconductors?
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a. a battery
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b. a capacitor
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c. a transistor
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d. a resistor

Ahot-air balloon takes off from the ground traveling vertically with a constant upward acceleration of magnitude g/4. after time interval δt, a crew member releases a ballast sandbag from the basket attached to the balloon. how many seconds does it take the sandbag to reach the ground? (express your answer in terms of δt)