Compare these two collisions of a pe student with a wall.
case a: a 75-kg pe student moving at 8 m/s collides with a padded wall and
stops.
case b: the same 75-kg pe student moving at 8 m/s collides with an unpadded
wall and stops
which variable is different for these two cases?
which case involves the greatest momentum change?
which case involves the greatest impulse?
which case involves the greatest force?

The variable in the two cases has been time of collision.

The change in momentum in both the cases has been equal.

The impulse in both the cases has been the same.

The greatest  force has been applied in case B.

The collision has been described as the contact of one body with another. There has been force of both the body that has been exerted with the collision.

The collision with padded wall has been softer, and is resulted with the longer duration of the collision. The collision with an unpadded wall has been hard and will be for a short duration of time.

The variable in the two cases has been time of collision.

Thus, the change in momentum in both the cases has been equal.

The change in momentum in with the cases has been the same. Thus, the impulse in both the cases has been the same.

The time of collision has been inversely proportional to force. Since, the time of collision has been longer for padded wall in Case A as compared to case B, the force has been smaller for case A.

Thus, the greatest  force has been applied in case B.

Learn more about collision, here:

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found in the nucleus

has mass of one amu