Aball is thrown straight up. what can be said about the sign of work done by the force exerted by gravity while the ball moves up and then down?
a) positive as the ball travels up, and positive as the ball travels down
b) zero as the ball travels up, and zero as the ball travels down
c) negative as the ball travels up, and negative as the ball travels down
d) positive as the ball travels up, and negative as the ball travels down
e) negative 'as the ball travels up, and positive as the ball travels down

If 21.2 kcals of energy is released by this reaction, how many kj does the reaction release? (1 cal 4.184 j)

The ultracentrifuge is an important tool for separating and analyzing proteins. because of the enormous centripetal accelerations, the centrifuge must be carefully balanced, with each sample matched by a sample of identical mass on the opposite side. any difference in the masses of opposing samples creates a net force on the shaft of the rotor, potentially leading to a catastrophic failure of the apparatus. suppose a scientist makes a slight error in sample preparation and one sample has a mass 10 mg larger than the opposing sample. if the samples are 12 cm from the axis of the rotor and the ultracentrifuge spins at 70,000 rpm, what is the magnitude of the net force on the rotor due to the unbalanced samples? ( be thorough on your answer)

Which magnetic property best describes a magnet’s ability to act at a distance? magnets are dipolar. magnets attract only certain objects. magnets have magnetic fields. magnets can transfer their properties to certain materials.