Gujarati
Hindi
7. MOTION
medium

$(a)$ Draw velocity-time graph for the following cases

$(i)$ When the object is at rest.

$(ii)$ When the object is thrown vertically upwards.

$(b)$ A motorcyclist riding motorcycle $A$ who is travelling at $36\, km h^{-1}$ applies the brakes and stops the motorcycle in $10\, s$. Another motorcyclist of motorcycle $B$ who is travelling at $18\, km h^{-1}$ applies the brakes and stops themotorcycle in $20\, s$. Plot speed-time graph for the two motorcycles. Which of the two motorcycles travelled farther before it come to a stop ?

Option A
Option B
Option C
Option D

Solution

For motorcycle $A$,

$u=36 km h ^{-1}$

$=\frac{36 \times 5}{18}=10 ms ^{-1}$

$v=0$

$t=10 s$

For motorcycle $B,$

$u=18 km h ^{-1}$

$=\frac{18 \times 5}{18}=5 ms ^{-1}$

$v=0$

$t=20 s$

Distance travelled by $A$ before stopping

$=$ Area of triangle $OPQ$

$=\frac{1}{2} \times 10 \times 10=50 m$

Distance travelled by $B$ before stopping

$=$ Area of triangle $OMN =\frac{1}{2} \times 20 \times 5=50 m$

Hence, both motorcycles travel same distance before they come to a stop.

Standard 9
Science

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