SPRING 2002 QUIZ 4

PHYSICS 100A 

1. A 15-g bullet with speed of 125m/s is shot into a 0.5-kg wood block originally at rest and embedded in the wood. What is the speed of the block after the shooting?

Solution.

Because the collision is perfect inelastic, the block and  the bullet have a common speed after collision. We have

                      mbulletvbullet + mblockvblock = (mbullet + mblock)V;

                     (15 x 10-3kg)(125m/s) + (0.5kg)(0) = (15 x 10-3kg + 0.5kg)V,

which gives V = 3.64m/s.

 2. A U-shaped tube with two ends open to the air is filled with mercury.  Find the pressure at the point A as shown. The density of mercury is 13.6 x 103kg/m3.                   

 

 We find the pressure from

          P = P0 + rHggh

              = 1.013 x 105N/m2 + (13.6 x 103kg/m3)(9.80m/s2)(2.5m)

              = 1.353 x 105N/m2 = 135.3kPa.