Chapter 6 Flashcards
What is NOT true about friction?
The force of static friction depends on the area of contact between the two surfaces.
Four identical blocks are moving on a surface for which the coefficient of kinetic friction between each block and the surface is Mk. The velocity of each block is indicated by the vector on the block. For which block is the force of friction between the surface and the block greatest?
The force of friction is the same for all four blocks.
A block of mass m is at rest on an inclined plane that makes an angle of 30 degrees as shown. Which statement is true about the force of static friction?
fs = mg sin 30 degrees
A heavy truck and light car have the same speed and same coefficients of static friction. Which vehicle will be able to stop in the shortest distance?
Both will be able to stop in the same distance
A block of wood is pulled by a horizontal string across a ROUGH surface at a CONSTANT velocity with a force of 20 N. The coefficient of kinetic friction between the surfaces is 0.3. The force of friction is
20 N
A mass m is placed on a ROUGH incline at an angle theta to the horizon. A force F is applied to the incline to PREVENT the mass from sliding. What is the direction of the frictional force?
Same direction as force F; up the hill
A mass m is placed on a rough incline at an angle theta to the horizon. A force F is applied up the incline so that the mass slides up the incline. What is the direction of the frictional force?
Opposite direction of force F; down the hill
A block of mass m is pulled in the direction shown in the figure across a rough surface. The MAGNITUDE of the frictional force is
Mk (mg - T sin theta)
A block of mass m is pulled in the direction shown in the figure across a rough surface with CONSTANT ACCELERATION. The MAGNITUDE of the frictional force is
T cos theta - ma
The SI units for the coefficient of friction are
None - friction is dimensionless
The block shown in the figures have EQUAL MASSES and are made of the same material. The VELOCITY is the same in each figure. The total frictional force exerted by the surface on the blcok is
The same in figure C (two blocks next to each other) and figure B (two blocks on top of each other)
Which free-body diagram best represents the forces acting on the student AT REST or SLIDING DOWN on the incline?
One arrow up and to the left, one arrow up and to the right, and one arrow straight down
If a jet plane doubles its speed, the drag force on the jet plane
Quadruples
As a sky diver falls through the air, her terminal speed
All of the above
(Depends on her mass, body’s orientation, the local value of the acceleration due to gravity, and the density of the air)
When a particle moves in a circle with constant speed, its acceleration is
Constant in magnitude
An object traveling in a circle at constant speed
Experiences an acceleration towards the center of the circle
A car going around a curve of radius R at a speed V experiences a centripetal acceleration ac. What is its acceleration if it goes around a curve of radius 3R at a speed of 2V?
(4/3)ac
Top view of ball on end of a string going counterclockwise. If the string breaks, the ball goes
Straight up from breakage site
Top view of ball on end of string going counterclockwise. Assume that air resistance is negligible. Which free-body diagram best represents the NET FORCE acting on the ball?
Arrow to the left
A block slides down a frictionless incline. The path at the bottom of the incline is an arc of a circle. The direction of the net force on the block at the bottom of the arc (point P) is along
Arrow straight up
A ball of mass m is attached to a thin string and whirled in a vertical circle or radius r. The tension in the string at point e where the ball is moving with speed v is
(mv^2)/r
