AP Physics 2-5 Example Problems 1. You can perform a popular trick by dropping a dollar bill (lengthwise) through the thumb and forefinger of a fellow student. Tell your fellow student to grab the dollar bill as fast as possible and she/he can have the dollar if they are able to catch it. (The length of a dollar bill is 15.7 cm and the average human reaction time is about 0.2 s. Is this proposal a good deal? Justify your answer. 2. The Petronas Twin Towers in Malaysia and the Chicago Sears Tower have heights of about 452 m and 443 m respectively. If objects were dropped from the top of each, what would be the difference in the time it takes the objects to reach the ground? 3. During the experiment mentioned in the text involving dropping a feather and a hammer on the Moon, both objects were released from a height of 1.30 m. According to the video of the experiment, they both took 1.26 s to hit the lunar surface. a) What is the local value for the acceleration due to gravity at that place on the Moon? b) What speed did the two objects reach just before hitting the lunar surface? 4. A photographer in a helicopter ascending vertically at a constant rate of 12.5 m/s accidentally drops a camera out the window when the helicopter is 60.0 m above the ground. a) How long will the camera take to reach the ground? b) What will its speed be when it hits? 5. Many highways with steep downhill areas have “run-away truck” inclined paths just off the main roadbed. These paths are designed so that if a vehicle’s braking system gives out, the driver can steer it onto this incline (usually composed of loose gravel). The idea is that the vehicle can then roll up the incline and come permanently and safely to a rest (in the gravel) with no need of a braking system. In one region of Hawaii the incline distance is 300 m and provides a constant deceleration of 2.50 m/s2. a) What is the maximum speed that a runaway vehicle can have as it enters the incline? b) How long would such a vehicle take to come to rest? c) Suppose another vehicle moving at 10 mi/h (4.47 m/s) faster than the maximum value enters the incline. What speed will it have as it leaves the gravel filled area?
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