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Exam 6: Force and Motion II

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Question 1

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A 12-kg crate rests on a horizontal surface and a boy pulls on it with a force that is 30 $\degree$ below the horizontal.If the coefficient of static friction is 0.40, the minimum magnitude force he needs to start the crate moving is:

A) 44 N
B) 47 N
C) 54 N
D) 56 N
E) 71 N

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Question 2

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A 5.0-kg crate is resting on a horizontal plank.The coefficient of static friction is 0.50 and the coefficient of kinetic friction is 0.40.After one end of the plank is raised so the plank makes an angle of 25 $\degree$ with the horizontal, the force of friction is:

A) 0 N
B) 20 N
C) 21 N
D) 22 N
E) 44 N

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Question 3

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A forward horizontal force of 12 N is used to pull a 240-N crate at constant velocity across a horizontal floor.The coefficient of friction is:

A brick slides on a horizontal surface.Which of the following will increase the frictional force on it?

A ball is thrown upward into the air with a speed that is greater than terminal speed.On the way up it slows down and, after its speed equals the terminal speed but before it gets to the top of its trajectory:

Block A, with a mass of 10 kg, rests on a 30 $\degree$ 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 8.0 kg, is attached to the dangling end of the string.The acceleration of B is:

A force (larger than the largest possible force of static friction) is applied to the left to an object moving to the right on a horizontal surface.Then:

The iron ball shown is being swung in a vertical circle at the end of a 0.7-m string.How slowly can the ball go through its top position without having the string go slack?

Block A, with mass m_A, is initially at rest on a horizontal floor.Block B, with mass m_B, is initially at rest on the horizontal top surface of A.The coefficient of static friction between the two blocks is $\mu$ _s.Block A is pulled with a horizontal force.It begins to slide out from under B if the force is greater than:

A 5.0-kg crate is on an incline that makes an angle 30 $\degree$ with the horizontal.If the coefficient of static friction is 0.5, the maximum force that can be applied parallel to the plane without moving the crate is:

If a satellite moves above the Earth's atmosphere in a circular orbit with constant speed, then:

The coefficient of kinetic friction:

A 5.0-kg crate is on an incline that makes an angle of 30 $\degree$ with the horizontal.If the coefficient of static friction is 0.50, the minimum force that can be applied parallel to the plane to hold the crate at rest is:

A professor holds an eraser against a vertical chalkboard by pushing horizontally on it.She pushes with a force that is much greater than is required to hold the eraser.The force of friction exerted by the board on the eraser increases if she:

Which of the following five graphs is correct for a particle moving in a circle of radius r at a constant speed of 10 m/s?

A crate is sliding down an incline that is 35 $\degree$ above the horizontal.If the coefficient of kinetic friction is 0.40, the acceleration of the crate is:

A 5.0-kg crate is resting on a horizontal plank.The coefficient of static friction is 0.50 and the coefficient of kinetic friction is 0.40.After one end of the plank is raised so the plank makes an angle of 30 $\degree$ with the horizontal, the force of friction is:

A ball of mass m is thrown downward from the edge of a cliff with an initial speed that is three times the terminal speed.Initially the drag force on it is

An object moves in a circle.If the mass is tripled, the speed halved and the radius unchanged then the magnitude of the centripetal force must be multiplied by a factor of:

At what angle should the roadway on a curve with a 50m radius be banked to allow cars to negotiate the curve at 12 m/s even if the roadway is icy (and the frictional force is zero) ?