Chapter 8 part I (Homework) Flashcards Preview

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Flashcards in Chapter 8 part I (Homework) Deck (10):
1

The blades in a blender rotate at a rate of 7900 rpm. When the motor is turned off during operation, the blades slow to rest in 3.0 s. What is the angular acceleration as the blades slow down?

-275.62 rad/s^2

2

A child rolls a ball on a level floor 4.0 m to another child. If the ball makes 18.0 revolutions, what is its diameter?

.07 m

3

A rotating merry go-round makes one complete revolution in 3.9 s.

(a) What is the linear speed of a child seated 1.1 m from the center?

(b) What is her acceleration (give components)?

tangential acceleration
radial acceleration

(a) 1.8 m/s

(b) tangential: 0 m/s^2
radial: 2.9 m/s^2 towards
the center

4

In traveling to the Moon, astronauts aboard the Apollo spacecraft put themselves into a slow rotation to distribute the Sun's energy evenly. At the start of their trip, they accelerated uniformly from no rotation to one revolution every minute during a 10 min time interval. The spacecraft can be thought of as a cylinder with a diameter of 9.2 m.

(a) Determine the angular acceleration.

(b) Determine the radial and tangential component (acc.) of the linear acceleration of a point on the skin of the ship 2.0 min after it started this acceleration.

(a) .000174 rad/s^2

(b) radial: .00202 m/s^2
tangential: .000802 m/s^2

5

The tires of a car make 85 revolutions as the car reduces its speed uniformly from 80 km/h to 50 km/h. The tires have a diameter of 0.80 m.

(a) What was the angular acceleration of the tires?

(b) If the car continues to decelerate at this rate, how much more time is required for it to stop?

(a) -1.76 rad/s^2

(b) 19.73 s

6

A small rubber wheel is used to drive a large pottery wheel, and they are mounted so that their circular edges touch. The small wheel has a radius of 2.0 cm and accelerates at the rate of 7.0 rad/s2, and it is in contact with the pottery wheel (radius 25.0 cm) without slipping.

(a) Calculate the angular acceleration of the pottery wheel.

(b) Calculate the time it takes the pottery wheel to reach its required speed of 60 rpm.

(a) .56 rad/s^2

(b) 11.21 s

7

Calculate the net torque about the axle of the wheel shown in the figure below. Assume that a friction torque of 0.40 m·N opposes the motion and that F = 16 N.

http://www.webassign.net/giancoli/8-39alt.gif

Magnitude (mN)

Direction (counter)clockwise

.92 mN

clockwise

8

The bolts on the cylinder head of an engine require tightening to a torque of 86 m·N.

http://www.webassign.net/giancoli/8-41alt.gif

If a wrench is L = 30 cm long, what force perpendicular to the wrench must the mechanic exert at its end?

If the six-sided bolt head is 15 mm in diameter, estimate the force applied near each of the six points by a socket wrench.

(a) 286.67 N

(b) 1911.11 N

9

A small 700 g ball on the end of a thin, light rod is rotated in a horizontal circle of radius 1.4 m.

(a) Calculate the moment of inertia of the ball about the center of the circle.

(b) Calculate the torque needed to keep the ball rotating at constant angular velocity if air resistance exerts a force of 0.025 N on the ball. Ignore the rod's moment of inertia and air resistance.

(a) 1.37 kg m^2

(b) .035 mN

10

A centrifuge rotor rotating at 14,000 rpm is shut off and is eventually brought uniformly to rest by a frictional torque of 1.10 m·N. If the mass of the rotor is 4.80 kg and it can be approximated as a solid cylinder of radius 0.0710 m, through

how many revolutions will the rotor turn before coming to rest?

How long will it take?

(a) 1880.26 rev

(b) 16.12 s