9. A 68.-kg surfer starts at the top of a wave at v = 1.5 m/s, drops a distance

Question

9. A 68.-kg surfer starts at the top of a wave at v = 1.5 m/s, drops a distance of 12 m (40 ft) to end with a speed of 23 m/s (52 mph). How much work was done on the surfer by the wave (show your work)? (*BONUS* What constant acceleration would get the surfer up to his final speed if his ride during the drop is actually 31 m?) 12.Two PasCars are at rest nose-to-nose. The red Pascar is 255 g, and the blue Pascar is 555 g. The spring gun of the red Pascar is fired giving a conservative horizontal push of 12.5 N for 0.150 s to the blue Pascar. What Is the magnitude of the final speed and momentum of each Pascar (show your work)?

Explanation / Answer

9)

a)

m=68 kg

work done =change in K.E

w=(1/2*m*v^2)-(1/2*m*u^2)

=1/2*m(v^2-u^2)

=1/2*68*(23^2-1.5^2)

=17909.5 J

b)

w=P.E

m*a*h=17909.5

a=17909.5/m*h

=17909.5/68*31

=8.496 m/sec^2

12)

here

momentum m*v=F*t

for red Pascar

255*10^-3*v=12.5*0.15

V=7.353 m/sec

and

momentum P=m*v=255*10^-3*7.353

=1.875 kg.m/sec

for blue Pascar

555*10^-3*v=12.5*0.15

V=3.378 m/sec

and

momentum P=m*v=555*10^-3*3.378

=1.875 kg.m/sec

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