2. A 22 cm diameter bowling ball dropped from a small airplane has a terminal sp

Question

2. A 22 cm diameter bowling ball dropped from a small airplane has a terminal speed of 77 m/s.

a. What is the cross-sectional area of the ball?

b. What drag force does the ball experience at this terminal speed?

c. What is the ball’s mass?

3. A 20 kg block rests on a table connected by a string to a 10 kg block.

a. Draw the picture. Draw a FBD for each of the blocks.

b. Find the minimum coefficient of static friction for which the blocks remain stationary.

c. Assume the coefficient of kinetic friction is half that of static friction. If the mass of the hanging block was increased to 15 kg, what would the acceleration of the system be?

Explanation / Answer

2) a)   cross sectional area = 3.14 * 0.11 * 0.11 = 0.038 m2

     b)    drag force does the ball experience =    1/2 * 1.225 * 77 * 77 * 0.47 * 0.038

                                                                    = 64.86 N

   c)    ball mass   = 64.86/9.8 = 6.62 kg

3)   a)   block on table have horizontal tension towards right and frictional force towards left

          hanging block have upwards tension and downwards force of gravity

    b)    Here, 10 * 9.8 = us * 20 * 9.8

=> us = 0.5

=> minimum coefficient of static friction   = 0.5

c)    Here,    15a = 15 * 9.8 - T

Also,      20a = T - 0.25 * 20 * 9.8

=> acceleration , a = 2.8 m/sec2

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