Friction
The SI unit for the coefficient of friction is..
It does not have a unit
A block of mass m is sliding across a rough surface. There is a coefficient of kinetic friction uk between the block and the surface. Which of the following represents the acceleration of the block?
- uk g
What are valid units of weight?
Hint: There are two answers
kg·m/s² and N
Two objects attract each other with a gravitational force of magnitude Fg1 If the distance between the centers of each object was increased to be three times the original distance, what would be the new magnitude of the gravitational force?
Fg1 / 9
A ball is rolling without slipping along the ground. Which type of friction force is acting on the ball?
Static Friction
A 15 kg block is sitting on a rough surface. The coefficient of static friction between the block and the surface is 0.5 and the coefficient of kinetic friction is 0.3. A 90 N force is then applied to the block, horizontal to the surface. What is the magnitude of the friction force acting on the block?
45 N Kinetic Friction only
The gravitational force between two objects depends on…
A) the mass of the first object
B) the distance between the center of each object
C) the mass of the second object
D) the radius of each object
A, B, and C
Planet A and planet B have masses of mA and mB and the distance between their centers is r1 If the mass of planet A is doubled and the mass of planet B is tripled, what would the new distance between their centers have to be (in terms of r1) for the gravitational force between the planets to remain the same?
/6 r1
A block is sliding across a rough table. Which of the following statements is true?
A) There is a friction force exerted on the table by the block, in the opposite direction as the block’s velocity
B) There is a friction force exerted on the block by the table, in the opposite direction as the block’s velocity
C) There is a friction force exerted on the table by the block, in the direction of the block’s velocity
B and C
A book is placed against a rough wall and a horizontal pushing force is applied to the book as shown on the right. Through experimentation it is determined that the minimum pushing force required to prevent the book from falling is 40 N. If the coefficient of static friction between the book and the wall is 0.6, what is the mass of the book?
2.4 kg
The variable g represents...
Hint: 2 answers
The acceleration due to gravity and The strength of a gravitational field
A new planet is discovered named “Planet X”. Based on careful observation, astronomers are able to determine that Planet X has mass of 8 x 10 23 kg and a radius of 2 x 10 6 m If an astronaut traveled to Planet X and dropped. a ball from rest from a height of 2 m, how long would it take to hit the ground (assuming the planet has no atmosphere and zero air resistance)?
0.55 seconds
A person is trying to push a heavy box across a rough floor. The magnitude of the force they have to apply to the box to get it moving (from rest) depends on which of the following? (select all that apply)
A) The coefficient of kinetic friction between the box and the floor
B) The mass of the box
C) The coefficient of static friction between the box and the floor
D) The gravitational acceleration g
A 25 kg block is sitting at rest on a rough surface of an incline as shown on the right. What is the magnitude of the friction force acting on the block? At 30 degrees.
125 N
Which of the following is required for a gravitational field to exist?
A) Two objects with different masses
B) Two objects with any mass
C) One object with a large mass
D) One object with any mass
D) One object with any mass
What is the magnitude of the gravitational force acting on the earth from the sun? Use 6 x 1024 kg for the mass of the earth, 2 x 1030 kg for the mass of the sun, and 1.5 x 1011 m for the distance between the center of the earth and the center of the sun.
F = 3.56 x 10 22 N
A person gathers together a stack of loose sheets of paper, places the stack against the wall and pushes on them with a force that is directly perpendicular to the wall. If they push hard enough, none of the sheets fall down. What is preventing the sheets of paper from falling?
A) An upwards vertical component of the applied pushing force which acts on all of the sheets
B) Static friction forces between the person’s hand, each of the sheets and the wall
C) A normal force acting on the sheets from the person’s hand and from the wall
B
A 12 N horizontal force acts on a 3 kg block which remains at rest on a rough surface. The coefficient of static friction between the block and the surface is 0.5. What is the magnitude of the friction force acting on the block?
A) 12 N B) 15 N
A) 12 N
Objects A, B and C have different masses and are different distances from object D. Object A has a mass of 2 kg and its center is 3 m away from the center of object D. Object B has a mass of 10 kg and its center is 8 m away from the center of object D. Object C has a mass of 6 kg and its center is 4 m away from object D. How do the forces exerted on object D by each of the other objects compare?
____ < ______ < _______
FB < FA < FC
How far above the surface of the earth would you have to be for your weight to be the same as it is on the surface of the moon? Use 6 x 10 24 kg for the mass of the earth, 6.4 x 10 6 m for the radius of the earth, 7.4 x 1022 kg for the mass of the moon and 1.7 x 106 m for the radius of the moon.
8.9 x 10 6 m