Practice 7E: | 1 | 2 | 3 | 4 |  Go up
Tangential speed - by Matt Henderson, 2003

1. A woman passes through a revolving door with a tangential speed of 1.8 m/s. If she is 0.80m from the center of the door, what is the door's angular speed? 

 v_t = 1.8 m/s and r = 0.8 m then we use the formula v_t = rw

1.8 = .8 (w) so w = 2.25 rad/s

(Table of contents)

2. A softball pitcher throws a ball with a tangential speed of 6.93 m/s. If the pitcher's arm is 0.660 m long, what is the angular speed of the ball before the pitcher releases it?

         v_t = 6.93 m/s and r = 0.660 m then we use the formula v_t = rw

        6.93 = .660 (w) so w = 10.5 rad/s

(Table of contents)

3. An athlete spins in a circle before releasing a discus with a tangential speed of 9.0 m/s. What is the angular speed of the spinning athlete? Assume the discus is .75m from the athlete's axis for rotation.

   v_t = 9.0 m/s and r = 0.75 m then we use the formula v_t = rw

        9.0 = .75 (w) so w = 12 rad/s

(Table of contents)

4. Fill in the unknown quantities in the following table:

On all the problems use the formula v_t = rw

            v_{t                    w}                       r

a.         ?            121.5 rad/s            0.030 m       v_t = .030 (121.5) so v_t = 3.645 m/s

b.     0.75 m/s          ?                      0.050 m     .75 = .050 (w) so w = 15 rad/s

c.         ?            1.2 turns/s                3.8 m      1.2 turns/s * 2p =  7.54 rad/s then plug that  into the 

formula  v_t = rw and you get  v_t = 3.8(7.54) so v_t = 29 m/s

d.     2.0p m/s     1.5p rad/s                    ?         2.0p = r(1.5p) so  r = 1.3 m

(Table of contents)