Quiz#1.

Always show the details of your solution.

Q1.      (a) The speed of light is 3.0x108 m/s.  Express this speed in mm/ps.  (1 ps = 10-12 s)

3x108 m/s = 3x108 m /s x [ 10-12 s /1ps ] x [103 mm / 1 m ]

= 3x108 x 10-12 x 103  mm/ps            =  0.3 mm/ps

(b) It takes 4 hours to drain a container of 1000 m3 of water. What is the “mass flow rate”, in kg/s, of water from the container? (density of water =103 kg/m3)

Mass flow rate = volume flow rate x density

=  [1000 m3/ 4h ] x [103 kg/m3] x [1h / 3600 s]

=  69.4 kg/s

Q2.      A ball is thrown directly upward with an initial speed of 20.0 m/s from a height   of 120 m above the ground.

Choose y to be positive upwards.

(a) Write down the values with the correct sign for vo , a  and yo.

vo = 20 m/s ;      a = - 9.8 m/s2 ;             yo = 120 m

(b) (i) At maximum height,  what is the velocity of the ball?

v = 0

(ii) At maximum height, what is the acceleration due to gravity? (Give the correct sign.)

a = - 9.8 m/s2

(c) What is the speed of the ball just before it hits the ground?

v2 = vo2 + 2 a ( y – yo) = (20)2 + 2 ( -9.8)( 0 – 120)

= 400+2352 = 2752

v = ± 52.5 m/s

Speed = 52.5 m/s