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<p>At t = 0 a 1.4 kg ball is thrown from the top of a tall tower with velocity = (13 m/s) +(30 m/s). What is ΔU of the ball-Earth system between t = 0 and t = 4.2 s (still free fall)?<br /><br />I tried using kinematics to find the position the ball would be at t=4.2 seconds. Then using the equation ΔU= mg(final height-inital height), I thought I found ΔU. What am I missing??</p>
<p>A 1200kg cannon fires a 100.0 kg cannonball at 83m/s. Whatis the recoil velocity of the cannon? Assume that frictional forcesare negligible and the cannon id firedhorizontally.</p><p>A. 83m/s   B. 7.6m/s  C. 8.3m/s   D. 6.9m/s</p>
Let ε0= 8 V, R = 3.0 , and L = 10.5 H. The switch is closed attime t = 0.At time t = 0.5 s, find the rate at which the battery suppliespower.A picture of the circuit can be found here:http://tinypic.com/view.php?pic=ekq3ih&s=7