Question

0.48 12. Two astronauts are m apart in their spaceship. One speaks to the other. The conversation is transmined to earth via electromagnetic waves. The time it takes for sound waves to travel at 343 m/'s through the air between the astronauts equals the time it takes for the electromagnetic waves to travel to the earth. How far away from the Earth is the spaceship? (a) 2.30 m (b) 790 m (c) 4.2x10m (d) 6.9x10Fm (e) 4.5x1010 m 13. Two converging lenses have the same focal length of 5.00 cm. They have a common principal axis and are separated by 24.8 cm. An object is located 10.0 cm to the left of the lefi-hand lens. What is the image distance (relative to the lens on the right) of the final image produced by this two-lens system? (a) 10.0 cm and upright (b) 10.0 cm and inverted (c) 7.55 cm and inverted (d) 7.55 cm and upright (e) -7.55 em and upright 14. An object is placed at a known distance in front of a mirror whose focal length is also known. You apply the mirror equation and find that the image distance is a negative number. This result tells you that all answers that are appropriate.) (Choose (a) The image is upright relative to the object. (b) The image is smaller than the object. (c) The image is virtual. (d) The image is real. (e) The image is larger than the object s. An electromagnetic wave is traveling in a vacuum. The electric field E of the wave is doubled. What happens to the magnetic field B, the total energy density u, and the intensity S of the wave? (a) B doubles, u increases by a factor of four, S doubles (b) B increases by a factor of four, u increases by a factor of four, S increases by a factor of four (c) B doubles, u doubles, S doubles (d) B doubles, u increases by a factor of four, S increases by a factor of four (e) B doubles, u decreases by a factor of two, S decreases by a factor of two

Answer 1

12)

Given data,

Distance = 0.48 m

Speed = 343 m/s

We know that,

Time = Distance / speed

= 0.48 m / 343 m/s

= 1.39 x 10^-3 s

The distace between earth and spaceship is

             d = c t

= ( 3.0 x 10⁸ m/s) (1.39 x 10^-3 s)

= 4.17 x 10⁵ m

Option c is correct