A model rocket sits on the launch pad until its fuel is ignited, blasting the rocket upward. During the short time of blast-off, as the ignited fuel goes down, the rocket goes up because:
a. the fuel pushes on the ground.
b. air friction pushes on the escaping fuel.
c. the downward force of gravity is less than the downward momentum of the fuel.
d. of none of the above reasons.
d
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Place a 1-kilogram block of iron at 40°C into 1 kilogram of water at 20°C and the final temperature of the two becomes
A) less than 30°C. B) at or about 30°C. C) more than 30°C.
Two lenses, the first with focal length 10.0 cm and the second with focal length -12.5 cm, are separated by 20.0 cm. An object, 2.40 cm tall, is 15.0 cm in front of the first lens. Where is the final image?
A. 20.0 cm after the second lens B. 12.5 cm after the second lens C. 5.60 cm after the second lens D. 50.0 cm after the second lens E. 100 cm after the second lens
A 2.00 kg pendulum bob on a string 1.50 m long, is released with a velocity of 2.00 m/s when the support string makes an angle of 30.0 degrees with the vertical. What is the velocity of the bob at the bottom of the swing?
A. 4.32 
B. 4.00
C. 3.75
D. 3.04
E. 2.81
The ancient water erosion features on the surface of Mars suggest that the planet must have had a much
A) warmer, thinner atmosphere in the past B) cooler, thicker atmosphere in the past C) cooler, thinner atmosphere in the past D) warmer, thicker atmosphere in the past