Answer the following questions: [2 M]

Question 12 Marks

Acceleration is a vector quantity. Is force a vector quantity too?

Answer

Yes, acceleration and force both are vector quantities, because both can be expressed completely only when magnitude and direction are given and the quantity which needs direction and magnitude both is called a vector quantity.

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Question 22 Marks

The unit of acceleration is $m/s^2$, verify this.

Answer

$\text { Acceleration }=\frac{\text { Change in velocity }}{\text { Time taken for change }}$
$\text { Unit of velocity }= m / s .$
$\text { Unit of time }=\text { second }$
$\therefore a =\frac{ m / s }{ s }=\frac{ m }{ s \times s }$
$a=\frac{m}{s^2}$

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Question 32 Marks

See the diagram and calculate the Distance and Displacement travelled by the body from A to I.

Answer

Distance travelled =
A → B → C → D → E → F → G → H + I
= 5 + 7 + 6 + 3 + 5 + 4 + 6 + 5
= 41 m
Displacement = A → I in a straight line shortest distance
= 1m

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Question 42 Marks

A bus travelled 200 km in the first 3 hours and then 100 kms for the next one and a half hours and then 120 kms for the next one and a half hours. What is the average velocity of the bus if it has moved in a straight line for the whole journey.

Answer

$\begin{aligned} \text { Average velocity } & =\frac{\text { Total Distance }}{\text { Total time }} \\ & =\frac{200+100+120}{3+1.5+1.5} \\ & =\frac{420}{6}=70 km / hr .\end{aligned}$

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Question 52 Marks

A cart with mass 20 kg went 50 m in a straight line on a plain and smooth road when a force of 2 N was applied to it. How much work was done by the force?

Answer

Force (F) = 2 N
Displacement (s) = 50 m
Work done (W) = ?
W = Fs
= 2 × 50
W = 100 Joule

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Question 62 Marks

A force of 1000 N was applied to stop a car that was moving with a constant velocity. The car stopped after moving through 10m. How much is the work done?

Answer

Force (F) = 1000 N
displacement (s) = 10m
work done (W) = ?
W = Fs
= 1000 × 10
W = 10,000 Joule

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Question 72 Marks

A ball is rolling from A to D on a flat and smooth surface. Its speed is 2 cm/s. On reaching B, it was pushed continuously up to C. On reaching D from C, its speed had become 4 cm/s. It took 2 seconds for it to go from B to C. What is the acceleration of the ball as it goes from B to C.

Answer

As its initial and final positions are one and the same.
Initial Velocity = 2 cm/s.
Final Velocity = 4 cm/s
Time taken for the change in velocity from B to
D = 4 cm/s – 2 cm/s = 2 cm/s
$\begin{aligned} \text { Acceleration } & =\frac{\text { Change in velocity }}{\text { Time taken for change }} \\ & =\frac{2 cm / s }{2 \operatorname{cec}}=1 cm / s ^2\end{aligned}$

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