PHYS101 Intro Practice Problems
Here are some practice problems for you to work through.
And if you get stuck, start over and go through the tried and true steps of problem solving:
- Draw the problem, and identify important events and information. Divide the problem into separate parts/stages if necessary.
- Draw and label your axes!
- Write your knowns - in variable form.
Write your unknowns - in variable form. - Your known and unknown variables should help you what equations are solvable or not.
Finally, if you are still stuck, read and reread and rethink what the problem is telling you and asking. Sometimes things will be implied rather than explicitly stated!
If you need more or different kinds of problems, here's an external website with tons of practice
problems that you might find useful: http://www.solvephysics.com/index.html
In particular, see the problems by topic:
http://www.solvephysics.com/problems_laws_by_topic.shtml
Mapping our class to problems on that site...
Midterm 1: Kinematics
Midterm 2: Conservation laws, Dynamics (NOT springs, Hooke's law, circular motion/angular momentum, torque, or center of mass/moment of inertia)
Midterm 3: Dynamics (circular motion/angular momentum, torque, and center of mass/moment of inertia), Thermodynamics, Fluids and Elasticity
Final exam: Comprehensive, plus: Waves, Dynamics (springs, Hooke's law)
Dimensional analysis
1. What are the dimensions of Δxv/a ?
2. What are the dimensions of vt ?
3. What are the dimensions of the right and left sides
of the velocity vs. time motion equation, v = v0 + at ?
[solutions to all dimensional analysis problems]
Estimation
1. Rushing the Field
The WVU football team manages to get the winning touchdown and fans rush the field. Estimate how many people, standing still and packed closely, can squeeze onto a football field that has dimensions of 50 yards x 100 yards.
Estimate the total volume of a car (note: assume it's a rectangular prism).
[solution]
Kinematics: horizontal displacement, velocity, and acceleration.
1. Highway Driving (introductory)
a. How long will it take you to go 60 miles down the highway at 60 mph?
b. How much time will you save from the same trip if you speed at 75 mph instead?
c. Draw the motion graphs for cars driving 60 and 75 miles per hour for 60 miles.
2. Crumby Mouse (introductory)
A mouse walks out of its hole and 3m in a straight line to get a crumb of bread. It eats the crumb and then runs at 0.5 m/s directly back to its hole. How long does it take to get back to its hole?
3. Wooden Fortress (easy)
A bullet hitting plywood experiences an average deceleration of 2.0x106 m/s2. Let's say a bullet is going 400 m/s and hits a wooden fortress wall perpendicular to the surface.
a. How thick does the wood need to be to stop the bullet?
b. What if it hits the wood at 800 m/s; how thick would the wood need to be?
c. Draw a cartoon of the x(t), v(t), and a(t) graphs.
4. Clumsy Jogger (easy/moderate)
A jogger running at 6 mph drops her keys, and then comes to a stop within 2 seconds. She then walks back to get her keys. How far does she need to walk back to get the keys [assume constant acceleration]?
5. Racecars (moderate)
Two cars are at rest on the starting line of a racetrack 100km long. The flags go up and they start accelerating. Car 1 accelerates at 1.5 m/s2 and car 2 accelerates at twice that value. They continue accelerating until each reaches its maximum velocity of 150 km/h.
a. Which car hits the finish line first?
b. How much time does it take for each car to reach maximum v?
c. How much time elapses between the cars reaching the finish line?
d. Make a cartoon sketch of the v(t) and v(t) graphs.
[haven't written out the solution yet, but I soon will. If you get stuck, try: 1) solving conditions for one car first, and 2) do the problem-solving tips! Start with one question, draw it, and then try other parts of the question separately.]
Projectile Motion
1. Little penguin's big jump (intermediate)
A penguin runs horizontally off the top of an
iceberg at 3 m/s and hits the water at a
distance of 10m. How tall is the iceberg?