Question

1. A body covers 20 m in first second, 25 m in second and 45 m in third second. What is the

average speed of body ?

2. The volume of a wooden block is 10 cm3. If the density of the wood is 0.8 gcm-3 . Find the

mass of the wooden block.

3. If 159.9 g piece of iron has a density 7.8 gcm-3. What is the volume?​

Answer 1

Ans.1)

✏ Given

• In first sec, it covers 20m
• In second sec, it covers 25m
• In third sec, it covers 45m

✏ To Find

• Avg. speed of the body

✏ Solution

Total distance covered by body in 3 seconds is 90m.

$\sf \small\implies \: avg \: speed = \dfrac{total \: distance}{total \: taken \: time}$

$\sf \: \: \: \: \: \: \: \: \: \: = \dfrac{90}{3} m.s$

$\sf \: \: \: \: \: \: \: \: \: \: \boxed{\boxed{ \bf{\purple{= 30m/s}}}}$

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Ans.2)

✏ Given

• Volume(V) of wooden block = 10cm³
• Density(D) of the wood = 0.8 g/cm³

✏ To Find

• Mass(m) of the wooden block

✏ Solution

$\sf \implies \boxed{ \sf{mass = \dfrac{density}{volume} }}$

$\sf \: \: \: \: \: \: \: = 10 \times 0.8 \: g$

$\sf \: \: \: \: \: \: \: \: \: \: \boxed{\boxed{ \bf{\purple{= 8g}}}}$

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Ans.3)

✏ Given

• Density of Iron = 7.8 g/cm³
• Mass of iron = 159.9g

✏ To Find

• Volume of iron

✏ Solution

$\sf \implies \boxed{ \sf{volume = \dfrac{mass}{density} }}$

$\sf\: \: \: \: \: \: \: \: = \dfrac{159.9}{7.8} cm {}^{3}$

$\sf \: \: \: \: \: \: \: \: \: \: \boxed{\boxed{ \bf{\purple{= 20.5 {cm}^{3}}}}}$