Physics 125 – Test Review
1. This is a velocity vs time graph for an object moving along the x-axis. The particle starts at x = 0 m and moves for 4 seconds.
a. Draw an acceleration vs. time graph with correct numerical axes:
b. Draw a position vs. time graph It is not necessary for the y axis to be numerically correct, just the shape and the x axis:
2.
3. (This problem has 5 parts, a-e; please read all before starting). Santa parked his sleigh 7.1 m from the edge of a 30.00 roof. Unfortunately, the parking brake failed. Santa’s sleigh slid down the roof and landed on the ground. The sled’s coefficient of kinetic friction with the snowy roof is 0.12. The pictorial representation has been drawn for you at left. Consider Santa’s sled as it is sliding down the roof and before it actually falls off:
a. Draw a neat, legible, free body diagram for this situation with appropriate axes. Label the forces with the correct symbol, listed at the top of page 1.
b. Under the free body diagram, write out Newton’s 1st or 2nd Law in component form for both axes, based on your free-body diagram. DO NOT write ΣF on the left side of the equation. Instead, write out the appropriate force components, using the correct symbol, listed at the top of page 1. Use sin θ and cos θ (not just x and y) to show components of forces that are not along an axis. Write what is appropriate on the right side of the equation to show whether it is Newton’s 1st or 2nd Law. Indicate which force components are in the negative direction by using a minus sign.
c. What is the acceleration of Santa’s sled?
d. How fast was Santa’s sled going when it fell off the roof?
e. How much time did it take the sleigh to slide to the end of the roof?
4 (20). A rope tow does 2.10 x 104 J of work on an 80-kg man to pull him up 73 m up a snowy hill, starting from rest. A frictional force of 90 N exists between the snow and the man’s skis. The hill has an incline of 100. The rope is parallel to the slope. Note 73 m is the length of the slope, not the height of the hill!
a. Draw a pictorial representation showing initial and final conditions of speed (v) position (s) and height (h).
b. Draw a free-body diagram showing all forces on the skier, with appropriate axes:
c. Find the net work done by all non-conservative forces on the skier after being towed 73m.
d. If the skier starts at rest, what is his speed after being towed a distance of 73 m? Use the Work-Energy Theorem, and NOT Newton’s Law, to solve this problem:
From Chapter 9 (torque)
5. A wrecking ball (weight = 5400 N) is supported by a boom, which may be assumed to be uniform and has a weight of 3600 N. As the drawing shows, a support cable runs from the top of the boom to the tractor. The angle between the support cable and the horizontal is 32°, and the angle between the boom and the horizontal is 48°.
(a) Find the tension in the support cable.
1
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(b) Find the magnitude of the force exerted on the lower end of the boom by the hinge at point P.
2
6. The skateboarder in the drawing starts down the left side of the ramp with an initial speed of 5.4 m/s. Assume friction and air resistance are negligible.
a. Assume friction and air resistance are negligible. Are there any non-conservative forces exerted on the skateboarder? If so, do they do work on the skateboarder? Why or why not?
a. draw the free body diagram for the skateboarder, just before he leaves the ramp
b. b. What would be the height h of the highest point reached by the skateboarder on the right side of the ramp?
7.
v=ov = 6.8 m/s
(15)2. A solid steel sphere with a radius of 6.21 cm is suspended from a spring scale.
a. What is the scale reading when the sphere is weighed in air?
b. The block is lowered into a beaker of oil and completely submerged. Draw a free-body diagram, showing all the forces on the sphere.
c. What is the scale reading of the sphere when it is submerged in oil? Note centimeters are not SI units.
6. Much of the destructiveness of volcanoes is due to expanding gases escaping in an explosive manner. A CO2 bubble, located 70 meters below the surface, rises to the top of Mt. Kilauea, where the pressure is 1.01 x 105 Pa. The density of the lava is 3000 kg/m3. Assume that the temperature of gas in the bubble remains constant and find:
a) The pressure inside the bubble at depth (2.16 x 106 Pa)
b) the ratio of the bubble’s volume at the top to that at the bottom. (21.4)