What observation about light supported Einstein’s theory?

Explanation:

Do you mean the theory that space-time is defined by what's in it? And that mass warps space-time?

There are many instances where his observation turned out to be correct. The most popular one is the phenomena of gravitational lensing. We can see the light from stars that are actually behind the sun. The huge gravity of the sun bends space-time and this also bends light. We use gravitational lensing a the time when trying to see very distant stars or galaxies.

1.8 m/s

Explanation:

Draw a free body diagram of the block.  There are four forces:

Normal force Fn up.

Weight force mg down.

Applied force F to the east.

Friction force Fn μ to the west.

Sum the forces in the y direction:

∑F = ma

Fn − mg = 0

Fn = mg

Sum the forces in the x direction:

F − Fn μ = ma

F − mg μ = ma

a = (F − mg μ) / m

a = (12 N − 6 kg × 9.8 m/s² × 0.15) / 6 kg

a = 0.53 m/s²

Given:

Δx = 3 m

v₀ = 0 m/s

a = 0.53 m/s²

Find: v

v² = v₀² + 2aΔx

v² = (0 m/s)² + 2 (0.53 m/s²) (3 m)

v = 1.8 m/s