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home / study / science / physics / questions and answers / two cameras are placed 90 m apart along a highway, ... Question: Two cameras are placed 90 m apart along a highway,... Bookmark Two cameras are placed 90 m apart along a highway, with each camera taking a picture the moment a car passes the camera. The speed limit on the highway is 100 km/h. A car approaches the first camera. The motorist starts braking with constant acceleration of magnitude 3.5 m/s 2 as he passes the first camera and then maintains this constant acceleration until he has passed the second camera. The time stamps show that the time difference between the two photographs is 3.2 s. Given this information, find out whether the car had been speeding at the first camera, and how fast it is going when passing the second camera.

Explanation / Answer

time = 3.2 sec

distance (S) = 90 m

acceleration = -3.5 m/s2

S = ut + at^2 / 2

90 = 3.2 u - 3.5*3.2^2 /2

u = 107.92 m/s (speed at first camera)

v = u + at

v = 107.92 - 3.5*3.2

v = 96.72 m/s ( speed when passes second camera )

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