MIDTERM I

Physics 9, section C

April28, 2005

Problem 1. A mass of 50kg rests on a horizontal surface. The coefficient of of kinetic friction between the mass and the surface is μk=0.20. A force of 817N is applied to the mass at an angle above the horizontal of 36.9ο. What is the acceleration of the mass?

Problem 2. A man whose mass is 100kg is riding on a large Ferris wheel of radius 10 meters.

(a)  At how many revolutions per minute is the Ferris wheel revolving if the man feels weightless at the top of ride?

(b)  What force does his seat exert on him at the bottom of the ride at this speed of the wheel?

Problem 3. Masses m1 and m2 rest on the two equal sides of an isosceles triangle of angle θ whose base is horizontal. The masses are connected by a massless cord via a frictionless pulley at the apex of the triangle. If the coefficient of kinetic friction between the masses and the sides of the triangle is μk, at what angle θ would the masses slide in uniform motion? Take m2>m1.

Problem 4. A 40.0kg person is standing on a scale in an elevator moving down uniformly at 2.00m/s.

(a)  What is the weight of the person measured on the scale?

(b)  The elevator is stopped by uniform deceleration in 2.00s. What is the weight of the person measured by the scale during this deceleration?

Problem 5. A mass m is thrown vertically upward from the surface of the earth with speed v.

(a)  Compare the time it takes the mass to reach its highest point with the time it takes for it to travel from this point back to the ground.

(b)  What is the speed of the mass when it highs the ground on the way down?

Problem 6. A picture of mass 10kg is being hung from the midpoint of a cord whose ends are 1.00m apart. If the breaking tension of the cord is 98N, what is the shortest cord that will support the picture? Assume the cord is massless.