- C A plane mirror forms an image that is the same distance as the object to a
mirror, but behind the mirror. The distance from the image to the object is
equal to the distance of the object to the mirror (100 cm) and the mirror to
the image (100 cm). 100 cm + 100 cm = 200 cm.
- D The impulse delivered to the ball is equal to the ball’s change in
momentum, and the presence of the mitt does not change this, eliminating (A)
and (C). The extra area may decrease the pressure on the catcher’s hand, but
not the force, eliminating (B). The padding of the mitt causes the time during
which the ball comes to a stop to increase (just as an air bag increases the
time it takes for an automobile passenger involved in an accident to come to
a stop), which decreases the magnitude of the ball’s acceleration (since a =
Δv/Δt). A decrease in the magnitude of the acceleration means a decrease in
the magnitude of the force (since a = F/m).
- C The second postulate of Einstein’s theory of special relativity states that
the speed of light is a universal constant (c = 3 × 10^8 m/s), regardless of the
motion of the source or the detector. So despite the fact that the spaceship is
approaching the planet at a speed of c/2, occupants of the ship will still
measure the speed of light to be c. The time it takes the light pulse to travel a
distance of 4.5 × 10^8 m is
