Use the Force, Luke
Practice for our upcoming Forces midterm…
Results: The Force is strong in this one
Welcome to the dark side
Obi-Wan says: Remember Luke, all forces and accelerations have a magnitude and direction.
1. Young physicists in trouble...
Physics was born when Newton’s Mom asked him to go out and mow the lawn. “Isaac, how many times do I have to tell you?!” Desperate, little Newt appeals to physics for help. Not finding what he needs, he invents a new law, and tells his Mom “for me to mow the lawn would be physically impossible. You see Mom, if I were to push on the lawn mower; the lawn mower will push back on me with an equal and opposite force. These forces will cancel making it impossible for me to accelerate the lawn mower. Besides, my favorite TV show is on.” What did Mom say to point out the flaw in Newt’s reasoning? Draw a sketch of all the forces on the mower and state the condition that must be met for the mower to accelerate forward.
2. For each of the following situations sketch the major forces that act on the bowling ball/book. Be sure to color code your forces: green for gravity, red for normal, blue for push and orange for friction.
3. You are driving a car with has a mass m of 1200 kg down a steep road that is inclined at an angle q = 7.0o from the horizontal. You punch the accelerator to increase your speed. The road exerts a force of friction forward (parallel and down the incline) on your car of 3300 N. The force of air resistance acts backwards on your car and is 3600 N.
A) Find the acceleration of the car.
Step 1: F.B.D.
Step 2: Apply Newt’s 2nd Law
Step 3: Solve for the acceleration a (algebraically first, then plug in the numbers.)
B) You are traveling with a speed of 15 m/s down the incline when an earthquake hits and opens up a large crack 75 m ahead. You must increase your speed to 18 m/s by the time you reach the crack. Do you make it? Assume that your acceleration is constant and is the value you found in part A).
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