Ch 8

A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 25-cm mark. From this information, the mass of the meterstick is

1 kg

On a balanced seesaw, a boy three times as heavy as his partner sits

1/3 the distance from the fulcrum.

You can safely stand on the overhanging end of a heavy plank that rests on a table. How much overhang depends on your mass and the mass of the plank. If you can stand on the end of a plank that overhangs the edge of the supporting table 1/5 its total length, how massive is the plank compared to your mass?

2/3

If you're on a Ferris wheel at a carnival, seated 10 m from the Ferris wheel's axis that makes a complete rotation each minute, your linear speed is

62.8 m/min.

Why can't you stand with your heels and back to a wall and then bend over to touch your toes and return to your stand-up position?

A vertical line through the center of gravity of your body is in front of the tips of your toes, which is outside your support base.

Why doesn't the Leaning Tower of Pisa topple over?

A vertical line through the center of gravity passes inside its support base.

Consider three axes of rotation for a pencil: along the lead, at right angles to the lead at the middle, and at right angles to the lead at one end. Rate the rotational inertias about each axis from smallest to largest.

Axis along the lead, through the center, through one end

Calculate the tension in a horizontal string that whirls a 2.0-kg toy in a circle of radius 2.9m when it moves at 3.5m/s on an icy surface. Centripetal Force: F=mv^2/r

F = 8.4 N

Where is the center of mass of a hollow soccer ball?

In the center of the ball

As distance increases between most of the mass of an object and its center of rotation, how does rotational inertia change?

It increases.

Calculate the angular momentum of the person if the force of friction that keeps a 95-kg person sitting on the edge of a horizontal rotating platform when the person sits 2.5m from the center of the platform and has a tangential speed of 1.4m/s . Angular Momentum = mvr

L = 330 (kg⋅m^2)/s

How is a flywheel constructed to maximize its rotational inertia?

Most of the mass is concentrated far from the axis.

A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 12.5-cm mark. From this information, the mass of the meterstick is

NONE OF THE BELOW 3/4 kg. 1/2 kg. 1/4 kg. 1 kg.

If the string that holds a whirling can in its circular path breaks, what kind of force causes it to move in a straight- line path: centripetal, centrifugal, or no force? What law of physics supports your answer?

No force; Newton's first law

If you hang at rest by your hands from a long vertical rope, where is your center of gravity with respect to the rope?

Somewhere straight below where your hands grab the rope

On a rotating turntable, how do tangential speed and rotational speed vary with distance from the center?

Tangential speed increases with distance. Rotational speed is constant.

Which will have the greater acceleration rolling down an incline: a hoop or a solid disk? Why?

The solid disk will because the mass is closer to the axis of rotation.

When you whirl a can at the end of a string in a circular path, what is the direction of the force you exert on the can?

Toward the center of the circle

The famous Leaning Tower of Pisa doesn't topple over because its center of gravity is

above a place of support

If Earth had a pair of identical moons on opposite sides of the same circular orbit, the center of gravity of the double-moon-Earth system would be

at the center of the Earth.

You can swing your legs to and fro more frequently when your legs are

bent

A coin and a ring roll down an incline at the same time. The one to first reach the bottom is the

coin

The net force exerted on a car traveling in a circular path at constant speed is

directed toward the center of the curve.

Your pet hamster sits on a record player that has constant angular speed. If the hamster moves to a point twice as far from the center, then its linear speed

doubles

A flywheel's diameter is twice that of another of the same shape and mass. Rotational inertia of the larger flywheel is

four times greater

The tangential speed on the outer edge of a rotating carousel is _______.

greater than toward the center

When a twirling ice skater brings her arms inward, her rotational speed

increases

What are the units of measurement for tangential speed? For rotational speed?

m/s for tangential, RPM for rotational

Which of these animals has a quicker stride?

mouse

Which horse moves faster in m/s on a merry-go-round?

one near outer rail

When a rock tied to a string is whirled in a horizontal circle, doubling the speed _______.

quadruples the tension in the string

As you crawl toward the edge of a large freely-rotating horizontal turntable in a carnival funhouse, the angular momentum of you and the turntable

remains the same, but the revolutions per minute decrease.

Two people are balanced on a seesaw. If one person leans inward toward the center of the seesaw, that person's end of the seesaw tends to

rise

As a huge rotating cloud of particles in space gravitate together forming an increasingly dense ball, it shrinks in size and

rotates faster

A ring, a disk, and a solid sphere begin rolling down a hill together. Which reaches the bottom first?

sphere

The rotational inertia of your leg is greater when your leg is

straight

You can safely stand on the overhanging end of a heavy plank that rests on a table. How much overhang depends on your mass and the plank's mass. If you can stand on the end of a plank that overhangs the edge of the supporting table 1/4 its total length, how massive is the plank compared to your mass?

the same

To kick a football so it won't topple end over end, kick it so the force of impact extends

through its center of gravity.

Consider two flywheels of the same size and shape, but one with twice the mass. Rotational inertia of the more massive one is

two times greater

To rotate a stubborn screw, it is best to use a screwdriver that has a

wide handle

Which tin can will roll down an incline in the shortest time, one filled with water or one filled with ice? (Hint: water 'slides' inside the can.)

with water

Calculate the torque produced by a 56-N perpendicular force at the end of a 0.18-m-long wrench. Torque = Lever Arm × Force

τ = 10 Nm