Question

1). A metal disk with radius, r, is spinning with a constant angular velocity. A red magnet is placed on the disk at   $\frac{1}{2}r$ and a blue magnet is placed at r. If you compare the tangential speed of the two magnets,

a. the red magnet is going half as fast

b. the magnets are going the same speed

c. the blue magnet is going twice as fast

d. the blue magnet is going four times as fast

2). In the equation, $v=wr$ if is measured in meters and is measured in m/s, what are the unites of ?

a. radians

b. radians per second

c. revolutions

d. revolutions per second

e. (a) or (c) is correct

f. (b) or (d) is correct

Answer 1

(C) * Let r is the radius of the disc * Blue magnet is placed at r * Red magnet is placed at 1/2 r Equation for tangential velocity v_t = w times R Q_t rightarrow tangential velocity w rightarrow Angular velocity of the disc R rightarrow Radius of the rotating object from center For blue magnet R = r Therefore v_t_B = w times r ---1 For Red magnet R = 1/2 r v_t_R = w times (1/2 r) u_t_R = 1/2 w r ---2 1/2 u_t_B/u_t_R = w r/1/2 w r = 2 = > u_t_B = 2 times (u_t_R) that is tangential velocity of blue magnet is going as fast as Red so the answer is option (c) \r\n (b) In physics angular velocity w is defined as the rate of change of angular displacement 'theta' with respect