7, +-1 points SerCp95MC.007 My Notes Ask Your Teacher Mark and David are loading

Question

7, +-1 points SerCp95MC.007 My Notes Ask Your Teacher Mark and David are loading identical cement blocks onto David's pickup truck. Mark lifts his block straight up from the ground to the truck, whereas David slides his block up a ramp on massless, frictionless rollers. Which statement is true? Mark does more work than David. O David does more work than Mark. Mark and David do the same amount of work. None of these statements is necessarily true because of the angle of the incline is unknown None of these statements is necessarily true because the mass of one block is not given. Need Help? Talk to a Tuter 8, + 1 points SerCP95MC.009. My Notes Ask Your Teacher A certain truck has twice the mass of a car. Both are moving at the same speed. If the kinetic energy of the truck is K, what is the kinetic energy of the car? 2K 0.71K K/4 K/2 Need Help? Taik to Titer to a Tutor

Explanation / Answer

7. mark and david do same amount of work.

Explanation: the work done by either Mark and David equals the increase in the gravitational potential energy of the block as it is lifted from the ground to the truck bed. Because they lift identical blocks through the same vertical distance, they do equal amounts of work.

8.

KE = 0.5*mv^2

for truck

m = 2M, v = V

KEt = 0.5*2M*V^2 = MV^2

MV^2 = K

for car

m = M, v = V

KEc = 0.5*MV^2

from above MV^2 = K

KEc = 0.5*K = K/2

9. u = 8.5 m/sec

at maximum height v = 0

a = -g = -9.81

v^2 = u^2 + 2as

s = (v^2 - u^2)/2a

s = (0 - 8.5^2)/(-2*9.81) = 3.68 m

h = 3.7 m

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