A Few Sample Questions for the First Test in PC 241

1) Your cousin Yolanda has a small, decorative “sun-catcher” hanging by a string from the rear-view mirror in her Buick. While she’s driving you to the Cineplex, the light ahead turns red. Naturally Yolanda stops the car, which comes to rest from a speed of 20 m/s, during a braking time of 5 seconds.

a) What is the car’s acceleration during this time?

b) What is your acceleration during this time?

c) What is the net force on you during this time?

d) What forces act on you, producing this net force?

e) Consider the sun-catcher. Draw a picture of it during the braking process, and then draw a free-body (force) diagram for it.

f) What angle does the string (from which the sun-catcher hangs) make with the vertical?

2) Estimate one part of the cost of the war on terror. How many man-years (A man-year here means the amount of time a full-time worker puts into the job in a year.) do Americans invest per year in security checks at the airport?

3) You need to pull a piano into a U-Haul truck. The piano weighs 400 pounds, and you have a rope that will break if the tension in it exceeds 200 pounds. Naturally you decide to haul the piano up a ramp. If the coefficient of kinetic friction between the piano and the ramp is 0.3, and the floor of the truck is 2 feet above the ground, how long must the ramp be?

4) Frank, who weighs 180 pounds, stands on a bathroom scale in an elevator. The elevator descends from the fifth floor to the second floor, which is thirty meters below the fifth floor. This elevator has a cruising speed of 3 meters per second, and it reaches this speed in two seconds. From cruising speed it comes to a stop over an interval of 2 seconds. Make a list of the different readings on the bathroom scale, and the times during which these readings can be observed.

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