1,674 practice questions for CBSE Class 9 Science, organised by NCERT chapter (13 chapters). Every question includes a written explanation. Pick a chapter below, or try the samples first.
A stone is released from rest at the top of a tower of known height and falls freely with the uniform acceleration $g$. The time it takes to reach the ground is wanted. Which equation gives that time in one step?
A$s = ut + \frac{1}{2}at^{2}$
B$v^{2} = u^{2} + 2as$
C$a = \frac{v - u}{s}$
D$v = u + at$
Show answer and explanation
Correct answer: A - $s = ut + \frac{1}{2}at^{2}$
The known quantities are $u = 0$, $a = g$ and the height $s$, and the wanted quantity is $t$, so the equation containing all four is $s = ut + \tfrac{1}{2}at^{2}$. The equation $v = u + at$ also contains $t$ but needs the landing velocity, which is not given. The equation $v^{2} = u^{2} + 2as$ has no $t$ in it at all, and dividing a change in velocity by a distance does not define acceleration.
Q2
medium
A farming community grows nine traditional varieties of rice. Some tolerate drought, some resist pests and some grow in poor soil. Consider these two statements. (I) Growing many varieties lowers the risk that one bad season destroys the whole harvest. (II) The nine varieties together form part of the biodiversity of that region. Which is correct?
ABoth (I) and (II) are correct
BOnly (II) is correct
CNeither (I) nor (II) is correct
DOnly (I) is correct
Show answer and explanation
Correct answer: A - Both (I) and (II) are correct
Diversity within a crop spreads the risk, because if drought strikes, the drought-tolerant varieties still yield, which is why diversity strengthens food security. Variety among living forms of one crop is itself part of a region's biodiversity. Both statements therefore hold, and neither contradicts the other.
Q3
medium
A ball rolling down a straight slope speeds up uniformly from $3\ \text{m s}^{-1}$ to $15\ \text{m s}^{-1}$ with an acceleration of $4\ \text{m s}^{-2}$. How long does this take?
A$3\ \text{s}$
B$3.75\ \text{s}$
C$4.5\ \text{s}$
D$48\ \text{s}$
Show answer and explanation
Correct answer: A - $3\ \text{s}$
From $v = u + at$, the time is $\frac{15 - 3}{4} = \frac{12}{4} = 3\ \text{s}$. Adding the velocities instead of subtracting them gives $\frac{18}{4} = 4.5\ \text{s}$. Using only the final velocity gives $\frac{15}{4} = 3.75\ \text{s}$, which would be right only if the ball had started from rest, and $48\ \text{s}$ comes from multiplying by the acceleration instead of dividing.
Q4
medium
Which statement correctly contrasts the way a plant grows with the way a young mammal grows?
ANeither a plant nor a mammal makes any new cells once it has been formed
BA plant adds new cells all over its body, while a mammal grows only at the tips of its limbs
CA plant adds new cells mainly at a few special growing regions, while a mammal adds cells all over its body
DBoth a plant and a mammal add new cells only at the tips of their bodies
Show answer and explanation
Correct answer: C - A plant adds new cells mainly at a few special growing regions, while a mammal adds cells all over its body
Plant growth is limited to regions of dividing cells, such as the tips of roots and shoots, while a growing mammal makes new cells throughout its body. Reversing this would give the plant uniform growth, which is not what happens. A mammal does not grow only at the tips of its limbs. Both plants and animals keep making new cells, for growth and for repair.
Q5
medium
Why are bryophytes called the amphibians of the plant kingdom?
AThey can change from a plant form into an animal form
BThey grow on land but still need water for reproduction
CThey possess both gills and lungs at different stages of life
DThey live in water but come out on to land in order to reproduce
Show answer and explanation
Correct answer: B - They grow on land but still need water for reproduction
Bryophytes grow on damp land, yet their male reproductive cells must swim through a film of water to reach the female cells, so like amphibians they remain tied to moisture. They are not aquatic plants that come ashore to breed. A plant never turns into an animal, and gills and lungs are animal organs.
Q6
medium
Mangoes, peas and tomatoes all carry their seeds inside a fleshy or pod-like covering. What is the main advantage of this to the plant?
AThe covering lets the seed photosynthesise and store extra food before it germinates
BThe covering removes the need for the plant to produce flowers
CThe covering protects the seeds and helps animals carry them away to new places
DThe covering allows fertilisation to take place in the water held inside the fruit
Show answer and explanation
Correct answer: C - The covering protects the seeds and helps animals carry them away to new places
A fruit shields the developing seeds and, when eaten or carried off by animals, spreads them far from the parent plant. A seed inside a fruit is not photosynthesising. Fruits develop from flowers rather than replacing them, and angiosperm fertilisation does not depend on water at all.
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