Silver and mercury are less reactive than copper and as copper will displace those metals from its salt solution which are less reactive than it.

Metals placed below the hydrogen in reactivity series, will not give H₂(g) with water (H₂O). Decreasing order of reactivity of metals is Na > Mg > Zn > Cu

a = dv/dt The increase in speed = (30 -12) = 18 m/s. Then, A = 18/15 = 1.2 metre per second square

In constant speed, acceleration does not change. So, it covers equal distances in equal time intervals.