Download Dynamics Exam Extra Credit

Dynamics Exam Extra Credit
Name:____________________ Class:__________
1. Define each of the following terms, and give units where appropriate:
o
o
o
o
o
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Mass
Inertia
Net force
Force
Weight
equilibrium
2. A young girl slides down a rope. As she slides faster and faster, she tightens her grip, increasing the force exerted on
her by the rope. What happens when this force is equal in magnitude to her weight? Explain.
Felicia, the ballet dancer, has a mass of 45.0 kg. a) What is Felicia’s weight on Earth? b) What is Felicia’s mass on
Jupiter, where the acceleration due to gravity is 25.0 m/s2? c) What is Felicia’s weight on Jupiter?
3.
4. Suppose you jump from the cliffs of Acapulco and perform a perfect swan dive. As you fall you exert an upward force
on the earth equal in magnitude to the downward force the earth exerts on you. Why, then, does it seem that you are
the one doing all the accelerating?
5. An object falling through the sky at a constant speed of 15 m/s experiences two forces: gravity and air resistance.
Which force is greater? How do you know?
6. A 30.0-g arrow is shot by William Tell through an 8.00-cm-thick apple sitting on top of his son’s head. If the arrow
enters the apple at 30.0 m/s and emerges at 25.0 m/s in the same direction, with what force has the apple resisted the
arrow?
7. The following forces act on an 10kg object: 10 N north, 50 N south, and 40 N west.
a) Draw a free-body diagram.
b) Determine the net force.
C) Determine the acceleration of the object.
a) What is the net force acting on a 25-N freely falling object?
8.
b) What is the net force when the object encounters 15 N of air resistance?
c) What is the force of air resistance the object encounters if it is accelerating at a rate of 3.8 m/s 2
downward?
d) What is the force of air resistance if the object has reached terminal velocity?
9. A boy applies a 12N horizontal force to a 44 N sled, causing it to move with an acceleration of 1.5 m/s2 across the
snow. What is the force of friction? What is the coefficient of friction between the sled and the snow?
10. What force would a scale in an elevator on Earth exert on a 53-kg person standing on it during the following
situations?
a.
b.
c.
d.
d.
The elevator moves up at constant speed.
The elevator moves down at constant speed.
It slows at 2.0 m/s2 while moving upward.
It speeds up at 2.0 m/s2 while moving downward.
The elevator slows to a stop while moving downward with a constant acceleration of 2.5 m/s2.
11. In her physics lab, Molly puts a 1.0-kg mass on a 2.0-kg block of wood. She pulls the combination across another
wooden board with a constant speed to determine the coefficient of sliding friction between the two surfaces. If Molly
must pull with a force of 6.0 N, what coefficient of sliding friction does she calculate for wood on wood?
12. A 12-kg crate rests on a horizontal surface and a boy pulls on it with a force that is 300 above the horizontal. Friction is present.
a) Draw a free body diagram. Be sure that all forces are clearly labeled and are resolved into x- and y- components. (5 pts)
b) Write the Fnet equations for the x- and y-directions. (Assume that the crate is not yet moving) (2 pts)
c) If the coefficient of static friction is 0.40, the minimum magnitude force he needs to start the crate moving is: (2 pts)
d
13. A 25-N crate slides down a frictionless incline that is 250 above the horizontal.
a) Draw a free body diagram. Be sure that all forces are clearly labeled and are resolved into x- and y- components.
b) Write the Fnet equations for the x- and y-directions.
c) What is the acceleration of the block?
14. Two forces act on a 16-kg object. The first force has a magnitude of 68 N and is directed 24° north of east. The second force is 32 N, 48°
north of west. What is the acceleration of the object resulting from the action of these two forces?
15. A 32-N force, parallel to the incline, is required to push a certain crate at constant velocity up a frictionless incline that is 300 above the
horizontal. The mass of the crate is:
16. A 400-N block is dragged along a rough (k = 0.4) horizontal surface by an applied force F as shown. The block moves at constant
velocity. The magnitude of F is:
17. A clerk moves a box of cans down an aisle by pulling on a strap attached to the box. The clerk pulls with a force of 185.0 N at an angle of 25.0
degrees from the horizontal. The box has a mass of 35.0 kg, and the coefficient of kinetic friction between the box and the floor is 0.450.
Find the acceleration of the box.
18. A 20.0-kg package is dropped from a high tower in still air and is "tracked" by a radar system. When the package is 25 m above the ground,
the radar tracking indicates that its acceleration is 7.0 m/s2. Determine the force of air resistance on the package.
19. A system of two cables supports a 150-N ball as shown.
a) What is the tension in the right-hand cable?
b) What is the tension in the horizontal cable?
20. Two blocks are connected by a weightless string and pulley on a frictionless table, as shown below. When the
blocks are released, B begins to fall downward. The block on the table, M, is 5 N and the block hanging of the table,
m, is 3 N.
a) Draw the FBD, resolving vectors into
components, if necessary. (5 pts)
b) Write your Fnet equations. (2 pts)
c) What is the acceleration of the blocks? What is the tension in the rope?
21. Block A, with a mass of 20 kg, rests on a 30 incline. The coefficient of kinetic friction is 0.20. The attached string is
parallel to the incline and passes over a massless, frictionless pulley at the top. Block B, with a mass of 30.0 kg,
is attached to the dangling end of the string. Object A is moving up the incline.
a) Draw free body diagrams
b) Find tension force in the string
c) Find the acceleration of object B
22.
23. Calculate the force of gravity between Earth (mass = 6.0 x 1024 kg) and the moon (mass = 7.4 x 1022 kg). The average Earth—moon distance is
3.8 x 108 m.
24.
25.
Many people mistakenly believe that the astronauts that orbit Earth are “above gravity” Calculate g for space shuttle territory; 200 km
above Earth’s surface. Assume Earth’s mass is 6.0 x 1024 kg, and its radius is 6.38 x 106 m (6380 km). Your answer is what percentage of
9.8 m/s2?
On the small and good planet Ballonius in a distant solar system, suppose we find the radius of the good planet to be 200 000 m. We also drop a
rock and find that it travels 1.5 m in the first second of free fail, which means it accelerates at 3 m/s2. Estimate the mass of Ballonius.