Skater with a mass of 50.0 kg slides across an icy pond with negligible friction. As he approaches a
friend, both he and his friend hold out their hands,
and the friend exerts a force in the direction oppo-
site to the skater's movement, which slows the skat-
er's speed from 2.0 m/s to 1.0 m/s. What is the
change in the skater's kinetic energy?
A. –25 J
C. – 100J
B. -75J
D. -150J​

B

Explanation:

Calculate the kinetic energy before and after they hold hands. Then, to find the change in kinetic energy simply subtract the final KE by initial KE.

GAIA is composed of the astrometry instrument, the photo-metric instrument, and the radial-velocity spectrometer.

Option C

Explanation:

European Space Agency have formed an observatory in 2013 related to space and it is named as GAIA. Mostly that observatory is designed from astrometry. Astrometry is the measure of positions, distances and motion of stars. So the payload of GAIA is composed of three main parts.

They are astrometry instrument for finding the location of stars, photo-metric instrument for luminous measurements and radial velocity spectrometer for velocity measurement. So all the three instruments were used to analyze the position, brightness and speed of the motion of stars in the space.