Answer:C
Explanation:
When a constant horizontal force is applied to the box, box started moving in the horizontal direction such that it moves with constant velocity 
Constant velocity implies that net force on the box is zero
i.e. there must be an opposing force which is equal to the applied force and friction force can serve that purpose.
So option c is the correct choice.
Answer:
2.5 m/s
Explanation:
There are calculators online that can help you easily calculate the accerlation.
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Answer
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The impulse on the second trial is smaller is smaller than in the first trial.
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Impose of a body is that change in momentum during a time interval. If the change of momentum takes longer then, the impulse of a force is less. I a moving object hits a hard surface the rate of change of momentum is very high. e.i in the first trial, the egg breaks because it hits the hard surface(ground).
In the second trial, the foam cushion absorbs the shock and prolongs the time of impact with the egg hence decreasing the impulse.
There is not enough information given to answer with. The force of gravity at the planet's surface depends on the planet's radius as well as its mass. The planet could have exactly the same mass as Earth has. But if it's radius is only 71% of Earth's radius, then gravity on its surface will be twice as strong as gravity on Earth.
If the substance doesn't change chemically, it is a physical reaction.
