If an object moved at 30.0 m/s and at a later time covers half the distance in the same time, calculate its new speed.

15 m/s

Explanation:

Let in time t the object moves a distance d with speed 30 m/s.

Again in time t, it covers half of distance and the new speed is v.

So, d = 30 x t (1)

d/2 = v x t

Put d = 30 t from equation (1)

30 x t / 2 = v x t

v = 15 m/s

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conservation of mass

mass before something happens = mass afterwards