Question

A car is moving with velocity 60 kilometre per hour is brought to rest in 20 seconds by applying brakes calculate the acceleration.

Answer 1

here negative sign indicate that acceleration is acting opposite direction.

Answer 2

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A car is moving with a velocity of 60 km/h is brought to rest in 20 seconds by applying brake find acceleration ?

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$\textsf{Acceleration = \sf - 0.83 \: m {s}^{ - 2} }$

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Initial Velocity ( u ) = 60 Km/h

Final Velocity ( v ) = 0 m/s ( At rest )

Time taken ( t ) = 20 s

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Acceleration of car ( a ) .

$\green{ \large \underline{ \mathbb{\underline{ EQUATION \: OF \: MOTION \: USED : }}}}$

$\purple{ \boxed{ \sf \: v = u + at \: }}$

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$\red{\textsf{ \underline{\underline{Converting velocity into m { \sf s}^{ - 1} : }}}}$

$\begin{array}{l} \hline \\ \small \displaystyle \sf \longrightarrow u = \frac{60 \:km}{ h} \times \frac{1000 \: m}{1 \: km} \times \frac{1 \: h}{60 \:min} \times \frac{1 \:min}{60 \:s} \\ \\\small \displaystyle \sf \longrightarrow u = \frac{600 \cancel{00 }\:m}{36 \cancel{00} \:s} \\ \\ \small \displaystyle \sf \longrightarrow u = \frac{600 \:m}{36 \: s} \\ \\\small \displaystyle \sf \longrightarrow u = 16.67 \: m {s}^{ - 1} \\ \\ \hline \end{array}$

$\begin{array}{l} \hline \\ \displaystyle \sf \longrightarrow v = u + at \\ \\ \displaystyle \sf \longrightarrow 0 =16.67 + a(20) \\ \\ \displaystyle \sf \longrightarrow 0 =16.67+ 20a \\ \\ \displaystyle \sf \longrightarrow 16.67 + 20a = 0 \\ \\ \displaystyle \sf \longrightarrow 20a = - 16.67 \\ \\ \displaystyle \sf \longrightarrow a = \frac{ - 16.67}{20} \\ \\ \displaystyle \sf \longrightarrow a = - 0.83 \: m {s}^{ - 2} \: \: \: \: \: \: \: \:\:\: \:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\: \: \: \: \: \: \: \: \: \: \: \: \\ \\ \hline \end{array}$

$\purple{ \boxed{ \textsf{Acceleration of car} \sf \:= -0.83 \: m {s}^{ - 2} \: \: \: \: }}$

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• Acceleration

Acceleration is the rate at which velocity changes with time . Acceleration can be negative , positive or zero . Negative acceleration is called retardation .

• Initial Velocity

Initial velocity is the velocity of the object before the effect of acceleration .

• Final Velocity

Final velocity is the velocity of the object after the effect of acceleration .

$\Large{\purple{\boxed{\begin{array}{l} \textsf{Equations of motion : } \\ \\ \textsf{v = u + at} \\ \\ \displaystyle\textsf{s = ut + \sf\frac{1}{2}a {t}^{2} } \\ \\ \sf {v}^{2} - {u}^{2} = 2as \end{array}}}}$