Concept explainers
A damaged 1200-kg car is being towed by a truck. Neglecting the friction, air drag, and rolling resistance, determine the extra power required (a) for constant velocity on a level road, (b) for constant velocity of 50 km/h on a 30° (from horizontal) uphill road, and (c) to accelerate on a level road from stop to 90 km/h in 12 s.
(a)
The extra power required for constant velocity on a level road.
Answer to Problem 34P
The extra power required for constant velocity on a level road is
Explanation of Solution
Write the equation of total power required during the rates of changes in potential and kinetic energies.
Here, the power needed to acceleate the body is
Conclusion:
Since the velocity is constant on a level road, the extra power required will be considered as zero.
Thus, the extra power required for constant velocity on a level road is
(b)
The extra power required for constant velocity of 50 km/h on a
Answer to Problem 34P
The extra power required for constant velocity of 50 km/h on a
Explanation of Solution
Calculate the value of
Here, mass of a damaged car is m, acceleration due to gravity is g, difference between the elevation of ski lift is
Conclusion:
Since the velocity is constant on a level road, the extra power needed to acceleate the body is considered as zero.
Substitute 1200 kg for m,
Substitute 0 for
Thus, the extra power required for constant velocity of 50 km/h on a
(c)
The extra power required to accelerate on a level road from stop to 90 km/h in 12 s.
Answer to Problem 34P
The extra power required to accelerate on a level road from stop to 90 km/h in 12 s is
Explanation of Solution
Calculate the value of
Here, initial and final velocity of a car is
Conclusion:
Since the car is accelerated on a level road, the value of
Substitute 1200 kg for m, 12 s for
Substitute 0 for
Thus, the extra power required to accelerate on a level road from stop to 90 km/h in 12 s is
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