Motion Module 1 - Regular
Questions and Problems
Linear Motion
1.A physics teacher who lives 30 miles from school is frustrated by the low speed limit of 65 mph. He decides to go 80 mph instead. How many minutes of time does he save driving at the higher speed?
2.Yourparents are those helicopter-like parents who want to control every event in your life and you’re trying to prove to them that the college you want to go to isn’t that long a drive from home. You tell them to watch their clocks as you leave from home and head toward the college, telling them that you will call when you arrive. You speed off at 70 MPH for 100 miles, but then the weather turns bad and you slow it down to 50 MPH for the remainder of the trip. You make it from home to your college in 3.0 hours exactly.
a. How far is your college from home?
b. What was your average speed for the trip?
3.A car drives for 1.5 hours at 60 mph east. Then the driver rests for an hour. Finally, the car drives for 3.0 hours at 40 mph south. Determine the average speed for the trip. 38.2 mph
4.One of the methods that the Washington D.C. Police Department uses to catch speeders is to trigger multiple photographs of cars that pass through an automated radar zone at excessive speed. The photographs below were taken 0.20 s apart. The marker lines are five feet apart. The speed limit in this zone was 45 mph. By how much was this car exceeding the speed limit?
For the remaining problems show all givens at the beginning of the solution.
5.The Boeing 747 can take up to 75 seconds to reach its takeoff speed of approximately 90 m/s. What is its average acceleration during takeoff? 1.2 m/s2
6.In getting ready to slam-dunk the ball, a basketball layer starts from rest and sprints to a speed of 6.0 m/s in
1.5 s. Assuming that the player accelerates uniformly, determine the distance that he runs.
7.A jetliner is landing with a speed of 69 m/s. Once the jet touches down, it has 750 m of runway in which to reduce its speed to 6.1 m/s. What is the average acceleration of the plane during landing?
8.A truck, traveling at a velocity of 33 m/s, comes to a halt by decelerating at 11 m/s2. How far does the truck travel in the process of stopping?
9.The length of the barrel of a primitive blowgun is 1.2 m. Upon leaving the barrel, a dart has a speed of 14 m/s. Assuming that the dart is uniformly accelerated, how long does it take for the dart to travel the length of the barrel?
10.A soccer player runs at a constant speed of 2.6m/s. For the next 18m, he speeds up with an acceleration of 0.45m/s2. What is his speed at the end of the run?
11.In a 100-m race, a sprinter explodes out of the starting block with an acceleration of 3.2 m/s2, which she sustains for 3.0 s. Then, her acceleration drops to zero for the rest of the race. What is her total time for the race?
12.Suppose a car is traveling at 12.0 m/s, and the driver sees a big baggy of crack cocaine in the lane of traffic. The guy is crack addict and needs a fix, so he decides to take advantage of the free crack cocaine. After 0.510 s has elapsed (the reaction time) the driver applies the brakes, and the car slows at a rate of 6.20 m/s2. What is the stopping distance of the car, as measured from the point where the driver first notices the crack cocaine?
13.A crack cocaine dealer is getting on the freeway (starting from rest) and trying to get away from some thugs to whom he sold bad dope. He initially accelerates at 4.9 m/s2 for 10 seconds ... until he sees a Highway Patrol. Then he maintains his speed for another 30 s. How far did he travel during the entire episode?
LABETTE
Physics of a Plastic Toy Popper
Introduction
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Motion Module 1 - Regular
Once you understand a bit about the physics of motion, you look at toys much differently. You begin to look at toys critically, in terms of how many principles of physics they illustrate. A toy store becomes even more provocative and exciting than when you were a kid. The balloon that you blow up and release before tying off the end is obeying Newton’s Third Law of Motion. The spinning top that seems to defy gravity is an example of a rotating body obeying the Law of Conservation of Angular Momentum.
There used to be a toy store in Petaluma called Aunt Julie’s. It was owned by a man named Ken (that always seemed odd to me). Ken loved kids and he had a great toy store. A kid could walk into his store and, with just about any amount of money, find a toy. There were bins of toys with prices as low as five cents. One day I was in Aunt Julie’s and there was a bin of what looked like halves of small hollow, rubber balls (Figure 9.9a). They were called poppers. They only cost nine cents each so I bought them all. To play with one, you simply turn it inside out and then put it on a flat surface. After a few moments it pops up in the air about a meter or so. For some reason, they’re very addictive.
The seeming simplicity of the poppers is deceptive. They’re more complicated than you might think. There are actually two different accelerations that occur, one right after the other. Inverting the popper puts potential energy into it. As it restores itself to its original shape, the stored energy produces a force on the table and the popper very quickly accelerates from rest up to its takeoff speed from the table. That final speed for the first acceleration becomes the initial speed for the freefall acceleration that occurs next. Your job is to work backwards from the average maximum height of the popper to answer a number of questions about the motion of the popper, ultimately determining the time of the “pop.”
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Motion Module 1 - Regular
Purpose
To gain experience using the equations of motion as they apply to an accelerating object.
Procedure
Invert a toy popper onto the lab table (Figure 9.9b) and let it “pop” into the air several times, measuring its maximum height with a ruler or rulers each time.
Data
Maximum Height of Popper (m) /Average maximum height of popper: ______
Questions/Calculations (Show all work)
1.Calculate the initial speed of the popper.
(Check this with me before you move on.) 5 m/s
2.Calculate how fast the popper is moving after 0.20 s.
3 m/s
3.Calculate the time it takes to reach its maximum height.
0.5 s
4.Calculate how far the popper has risen in 0.30 s.
0.8 m
5.Let’s say that as soon as the popper popped, the table and floor disappeared. Calculate how long it would take the popper to reach a point 5.0 m below where it started.
1.5 s
6.If the inverted popper restores itself by pressing on the table through a distance of about 1.5 cm, calculate the acceleration of the popper as it pushes against the table.
800 m/s
7.Calculate the time of the pop.
.007 s
Questions and Problems
Linear Motion (continued)
1.In the song “The Ode to Billy Joe,” Bobbie Gentry sings about how Billy Joe Macallister and his girlfriend are seen dropping something suspicious off the Tallahatchie Bridge (I think it was a baby). Assume this “package” is in unrestricted freefall for 5.0 seconds and then (ouch) it hits the water.
a.What is the velocity of the “package” just before hitting the water?
-49 m/s
b.What is the displacement of the “package” during the fall?
-122.5 m
2.A United Airlines jet loses an engine and has to make an emergency landing on a little municipal runway. It lands, touching down on the runway with a speed of 72 m/s. Once the jet touches down, it has only
350 m of runway in which to reduce its speed to 5.0 m/s (a more typical runway length is 750 m). Calculate the average acceleration of the plane during landing and compare it to freefall acceleration.
-7.37 m/s2 75%
3.A ball is thrown straight down and accelerated by gravity. After 2.0 seconds, it is moving at 35 m/s. At what velocity was it originally thrown?
-15.4 m/s
4.A hotshot baseball pitcher throws a baseball vertically upward. 7.20 seconds later the ball has a downward velocity of 21.5 m/s. What was the velocity of the ball when the pitcher threw it?
49.1 m/s
5.A car moving at 18 m/s is slowed at a rate of 1.5 m/s2. How fast is it moving after 5.0 seconds? 9.5 m/s
6.The image to the right is an F/A 18 Hornet about to be launched from the deck of USS George Washington. You can see other images of aircraft carriers at During launch, the Hornet will attain a speed of 78 m/s over a distance of just 76 meters.
a.What acceleration is necessary for this to happen?
b.How much time will it take the F/A 18 Hornet to take off?
7.Talking on his cellphone while he’s driving, a guy doesn’t see a deer run out in the road in front of him. He’s traveling at 33 m/s and once he sees the deer, he slams on the brakes and is able to decelerate at 15 m/s2. If the deer is 35 m away when he starts braking, does he hit the deer?
8.A mean wife wants to collect on her husband’s life insurance policy so she invites him to the observation deck on top of a 95-story building, 427 m high. She coaxes him to look over – way over – the edge. Then she accidentally … “bumps” him.
a. Ignoring air resistance, what is the velocity of the guy when he strikes the ground?
-91.5 m/s
b. How much time does he have to think about how rotten his wife is?9.3 s
9.The school gets a new high-dive for the pool and the star diver gives it a try, springing upward with the initial speed of 2.2 m/s from the board (4.0 m above the water). What is his velocity when he strikes the water?
-9.1 m/s
10.Two girls with slingshots are on the top of a cliff scouting for birds. They see two, one straight up and one straight down. One girl fires a pebble straight up with an initial speed of 15 m/s and the other fires a pebble straight down with an initial speed of 9.0 m/s. How far apart are the two pebbles after 0.50 s?
12 m
11.A ball is thrown upward from the top of a 25.0m tall building. The ball's initial speed is 12.0m/s. At the same instant, a person is running on the ground at a distance of 31.0m from the building. What must be the average speed of the person if he is to catch the ball at the bottom of the building?
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