An Olympic high jumper wants to cross a bar 1.8 m off the ground. How fast does

Question

An Olympic high jumper wants to cross a bar 1.8 m off the ground. How fast does she have to run to accomplish this? 2.5 m/s 3.2m/s 4.0 m/s 5.9 m/s A train car collides with, and couples to, an identical car initially at rest. If the initial speed of the first car was v_0, what will be the final velocity of the cars after the collision? 0 v_0/2 v_0 2 v_0 A centrifuge accelerates uniformly from rest to 13,000 RPM in 85 s. Through how many revolutions did it turn in this time? 152 rev 9,200 rev 1,300 rev 58,000 rev

Explanation / Answer

6. using momentum conservation:

m1v1 + m2v2 = (m1+m2)*V

m1 = m2 = m

v2 = 0

v1 = v0

V = mv0/2m

V = v0/2

7.

13000 rpm = 13000/60 = 216.66 rav/sec

uniform acceleration means avg. revolution is 216.66/2 = 108.33

so in 85 sec total revolution is

rev = 108.33*85 = 9208.5 rev = 9200 rev

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