Answer: Heterogeneous mixture - the parts are not uniformly mixed.
A mixture contains components having distinct chemical properties. There are two types of mixtures: homogeneous and heterogeneous. In a homogeneous mixture there is uniform distribution of components. we cannot distinguish one portion of the mixture from another. for example salt mixed in water. In heterogeneous mixture, the components are not uniformly mixed. hence, we are able to distinguish different parts of a mixture, like the mixture of iron, sand and salt given in this question.
Explanation:
It is given that,
A particle starts from rest and has an acceleration function as :

(a) Since, 
v = velocity




(b) 
x = position



(c) Velocity function is given by :


t = 1 seconds
So, at t = 1 second the velocity of the particle is zero.
Answer:
v = 94m/s
Explanation:
Using the first equation of motion
v = u + at
u = 4m/s , a = 3m/s² , t = 30s , v = ?
v = u + at
v = 4 + 3 × 30
v = 4 + 90
v = 94m/s
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Lighting gives a sense of scale (The sky)