4. A driver travels 135 km, east in 1.5 h, stops for 45 minutes for lunch,
1 answer:
Answer:
The driver's average velocity is 82.35 km/h.
Explanation:
Given:
The motion of the driver can be divided into 3 parts:
i. Displacement of the driver in 1.5 hours = 135 km
ii. Rest for 45 minutes.
iii. Displacement in next 2 hours = 215 km
The direction of motion remains same (east).
Now, total displacement of the driver is, km.
Rest time is 45 minutes. Converting it to hours, we need to use the conversion factor hour.
So, 45 minutes in hours is equal to hours.
Now, total time taken for the complete journey is,
Average velocity is given as:
Therefore, the driver's average velocity is 82.35 km/h
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For the work-energy theorem, the work needed to stop the bus is equal to its variation of kinetic energy:
where
W is the work
Kf is the final kinetic energy of the bus
Ki is the initial kinetic energy of the bus
Since the bus comes at rest, its final kinetic energy is zero:
, so the work done by the brakes to stop the bus is
And the work done is negative, because the force applied by the brake is in the opposite direction to that of the bus motion.
where
W is the work
Kf is the final kinetic energy of the bus
Ki is the initial kinetic energy of the bus
Since the bus comes at rest, its final kinetic energy is zero:
And the work done is negative, because the force applied by the brake is in the opposite direction to that of the bus motion.