EXAM 3 (9-13)

A plumber pushes straight down on the end of a long wrench as shown. What is the magnitude of the torque he applies about the pipe at lower right?

(0.80 m)(900 N)cos 19°

A piece of thin uniform wire of mass m and length 3b is bent into an equilateral triangle. Find the moment of inertia of the wire triangle about an axis perpendicular to the plane of the triangle and passing through one of its vertices.

1/2 mb^2

A uniform solid sphere has a moment of inertia I about an axis tangent to its surface. What is the moment of inertia of this sphere about an axis through its center?

2/7 I

Planet Z-34 has a mass equal to 1/3 that of Earth, a radius equal to 1/3 that of Earth, and an axial spin rate 1/2 that of Earth. With g representing, as usual, the acceleration due to gravity on the surface of Earth, the acceleration due to gravity on the surface of Z-34 is

3g.

The four forces shown all have the same magnitude: F1 = F2 = F3 = F4. Which force produces the greatesttorque about the point O (marked by the blue dot)?

F1

A dump truck has a large cubical concrete block in its bed. The coefficients of friction between this block and the floor of the bed are µk = 0.450 and µs = 0.650. As the bed is slowly tilted above the horizontal, will the brick first begin to slide or will it first tip over?

It will first begin to slide.

A spinning figure skater pulls his arms in as he rotates on the ice. As he pulls his arms in, what happens to his angular momentum L and kinetic energy K?

L stays the same; K increases.

A baseball is located at the surface of the earth. Which statements about it are correct? (There may be more than one correct choice.)

The gravitational force on the ball due to the earth is exactly the same as the gravitational force on the earth due to the ball.

Suppose that a heavy person and a light person are balanced on a teeter-totter made of a plank of wood. Each person now moves in toward the fulcrum a distance of 25 cm. What effect will this have on the balance of the teeter-totter?

The light person's end will go down.

A small car has a head-on collision with a large truck. Which of the following statements concerning the magnitude of the average force due to the collision is correct?

The small car and the truck experience the same average force.

In an ELASTIC collision between two perfectly rigid objects

both the momentum and the kinetic energy of the system are conserved.

A glider of mass m1 on a frictionless horizontal track is connected to an object of mass m2 by a massless string. The glider accelerates to the right, the object accelerates downward, and the string rotates the pulley. What is the relationship among T1 (the tension in the horizontal part of the string), T2 (the tension in the vertical part of the string), and the weight m2g of the object?

m2g > T2 > T1

On a smooth horizontal floor, an object slides into a spring which is attached to another mass that is initially stationary. When the spring is most compressed, both objects are moving at the same speed. Ignoring friction, what is conserved during this interaction?

momentum and mechanical energy

The Young's modulus is the ratio of ................... within the elastic limit of the materials.

stress to strain

The Bulk's modulus is the ratio of ................. within the elastic limit of the materials.

stress to volume strain

Tensile stress is

the applied force per cross-sectional area.

The reason an astronaut in an earth satellite feels weightless is that

the astronaut is falling.

A solid bowling ball rolls down a ramp. Which of the following forces exerts a torque on the bowling ball about its center?

the friction force exerted by the ramp

A shell explodes into two fragments, one fragment 25 times heavier than the other. If any gas from the explosion has negligible mass, then

the momentum change of the lighter fragment is exactly the same as the momentum change of the heavier fragment.

In an INELASTIC collision between two objects

the momentum of the system is conserved but the kinetic energy of the system is not conserved.

Tensile strain is

the ratio of the change in length to the original length.

A disk and a sphere are released simultaneously at the top of an inclined plane. They roll down without slipping. Which will reach the bottom first?

the sphere

Archimedes' Principle state that, an object that is completely or partially submerged in a fluid experiences an upward buoyant force equal to

the weight of the fluid displaced.

A certain planet has an escape speed V. If another planet of the same size has twice the mass as the first planet, its escape speed will be

√2 v.

A lightweight string is wrapped several times around the rim of a small hoop. If the free end of the string is held in place and the hoop is released from rest, the string unwinds and the hoop descends. How does the tension in the string (T) compare to the weight of the hoop (w)?

T < w

A satellite of mass m has an orbital period T when it is in a circular orbit of radius R around the earth. If the satellite instead had mass 4m, its orbital period would be

T.

Pressure at any point in a fluid is

directly proportional to the density of the fluid and to the depth in the fluid.

Bernoulli's equation is a law of conservation of .................... applied to a fluid.

energy