www.solstation.com...
It has been estimated that the total mass of the Main Asteroid Belt may total less than 1/1000th of the mass of the Earth. Indeed, if all asteroids down to the size of meter- or yard-sized boulders or less were combined together, the resulting object would measure less than 1,300 to 1,500 km (810 to 930 miles) across, which is less than one third to one half the diameter of the Earth's Moon.

Originally posted by ArMaP
You can try to see what would happen with the Earth using the Earth Impact Effects Program

After some experiments I found that it is very difficult to destroy a planet of the size of the Earth.

www.lpl.arizona.edu...

Your Inputs:
Distance from Impact: 10000.00 km = 6210.00 miles
Projectile Diameter: 1700000.00 m = 5576000.00 ft = 1055.70 miles
Projectile Density: 1500 kg/m3
Impact Velocity: 240.00 km/s = 149.04 miles/s (Your chosen velocity is higher than the maximum for an object orbiting the sun)
Impact Angle: 30 degrees
Target Density: 1000 kg/m3
Target Type: Ice
Energy:
Energy before atmospheric entry: 1.11 x 1032 Joules = 2.65 x 1016 MegaTons TNT
The average interval between impacts of this size is longer than the Earth's age.
Such impacts could only occur during the accumulation of the Earth, between 4.5 and 4 billion years ago.
Major Global Changes:
The Earth is strongly disturbed by the impact, but loses little mass.
44.96 percent of the Earth is melted
The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis.
The impact does not shift the Earth's orbit noticeably.
Crater Dimensions:
What does this mean?



Transient Crater Diameter: 10800 km = 6690 miles
Transient Crater Depth: 3810 km = 2370 miles


Final Crater Diameter: 36200 km = 22500 miles
Final Crater Depth: 6.97 km = 4.33 miles
The final crater is replaced by a large, circular melt province.
At this impact velocity ( < 12 km/s), little shock melting of the target occurs.
Melt volume = 3.02 times the crater volume
At this size, the crater forms in its own melt pool.
Thermal Radiation:
What does this mean?



Time for maximum radiation: 401 seconds after impact


Your position is inside the fireball.
The fireball appears 2040 times larger than the sun
Thermal Exposure: 4.86 x 1014 Joules/m2
Duration of Irradiation: 1.25e+06 seconds
Radiant flux (relative to the sun): 389000


Effects of Thermal Radiation:


Clothing ignites

Much of the body suffers third degree burns

Newspaper ignites

Plywood flames

Deciduous trees ignite

Grass ignites



Seismic Effects:
What does this mean?


The major seismic shaking will arrive at approximately 2000 seconds.
Richter Scale Magnitude: 15.6 (This is greater than any earthquake in recorded history)
Mercalli Scale Intensity at a distance of 10000 km:


X. Most masonry and frame structures destroyed with their foundations. Some well-built wooden structures and bridges destroyed. Serious damage to dams, dikes, embankments. Large landslides. Water thrown on banks of canals, rivers, lakes, etc. Sand and mud shifted horizontally on beaches and flat land. Rails bent slightly.

XI. As X. Rails bent greatly. Underground pipelines completely out of service.


Ejecta:
What does this mean?



Little rocky ejecta reaches this site; fallout is dominated by condensed vapor from the projectile.


Air Blast:
What does this mean?


The air blast will arrive at approximately 30300 seconds.
Peak Overpressure: 1.61e+09 Pa = 16100 bars = 228000 psi
Max wind velocity: 32300 m/s = 72200 mph
Sound Intensity: 184 dB (Dangerously Loud)
Damage Description:


Multistory wall-bearing buildings will collapse.

Wood frame buildings will almost completely collapse.

Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse.

Highway truss bridges will collapse.

Highway girder bridges will collapse.

Glass windows will shatter.

Cars and trucks will be largely displaced and grossly distorted and will require rebuilding before use.

Up to 90 percent of trees blown down; remainder stripped of branches and leaves.