Kinematics

JEE Main level, numerical answer, medium

42 of 308

Question 42 of 308

A bus moving along a straight highway with speed of 72 km/h72 \mathrm{~km} / \mathrm{h} is brought to halt within 4s4 s after applying the brakes. The distance travelled by the bus during this time (Assume the retardation is uniform) is _____m.

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Answer: 40

 Initial velocity =u=72 km/h=20 m/sv=u+ at ⇒0=20+a×4a=−5 m/s2v2−u2=2 as ⇒02−202=2(−5).ss=40 m\begin{aligned} & \text { Initial velocity }=u=72 \mathrm{~km} / \mathrm{h}=20 \mathrm{~m} / \mathrm{s} \\ & \mathrm{v}=\mathrm{u}+\text { at } \\ & \Rightarrow 0=20+\mathrm{a} \times 4 \\ & \mathrm{a}=-5 \mathrm{~m} / \mathrm{s}^2 \\ & \mathrm{v}^2-\mathrm{u}^2=2 \text { as } \\ & \Rightarrow 0^2-20^2=2(-5) . \mathrm{s} \\ & \mathrm{s}=40 \mathrm{~m}\end{aligned}

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