Example Mid-Term

Here's some example mid-term questions. You should know the kinematic equations and "F=ma".

(1) A skateboarder skates down and up a semicircular ramp with a radius of 3 m. How fast is she going when she is right at the bottom of the ramp if she feels 50% heavier at that point?

(2) Explain why it is bad to lock the wheels of your car. Why does the car stop in a shorter distance if you do not allow the wheels to lock but keep the wheels spinning?

(3) Draw free body diagrams for the following situations. a) A ball that is being thrown straight up in the air. Draw the diagram at a time just before the ball leaves the throwers hand (ignore air resistance). b) A feather falling slowly to air(you must include air resistance in this one). c) A birdhouse hanging by a wire from a tree. The birdhouse has a squirrel sitting atop it. (Only draw the diagram for the birdhouse.)

(4) You try to slide a 50 kg couch across the floor by pulling it with a 300 N force applied 30° above the horizontal as shown below. If the coefficients of friction between the couch and the floor are 0.5 and 0.4 for statis and kinetic, respectively, find the force of friction acting on the couch. Justify your answer.

(5) A 200 g ball is attached to the end of a 1 m long string and whirled around in a circle. If the string makes an angle of 20° below the horizontal, what is the speed of the ball and what is the tension in the string?

(6) A projectile is fired from ground level with an initial speed of 55.6 m/s at an angle of 41.2° above the horizontal. (a) Determine the time necessary for the projectile to reach its maximum height. (b) Determine the maximum height reached by the projectile. (c) Determine the horizontal and vertical components of the velocity vector at the maximum height. (d) Determine the horizontal and vertical components of the acceleration vector at the maximum height.