A car of mass $$\(1400 \mathrm{~kg}\)$$ is moving along a straight horizontal road against a resistance of magnitude $$\(350 \mathrm{~N}\)$$. Find the acceleration of the car when its speed is $$\(20 \mathrm{~m} \mathrm{~s}^{-1}\)$$ and the engine is working at $$\(15 \mathrm{~kW}\)$$. ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................
Exam No：9709_w20_qp_41 Year：2020 Question No：2(b)
Answer:
\(15000=\mathrm{DF} \times 20 \quad[\mathrm{DF}=750]\)
\(\mathrm{DF}-350=1400 a\)
\(a=\frac{2}{7} \mathrm{~ms}^{-2}\)
\(\mathrm{DF}-350=1400 a\)
\(a=\frac{2}{7} \mathrm{~ms}^{-2}\)
Knowledge points:
4.5.4 use the definition of power as the rate at which a force does work, and use the relationship between power, force and velocity for a force acting in the direction of motion Including calculation of (average) power;P = Fv
4.5.5 solve problems involving, for example, the instantaneous acceleration of a car moving on a hill
Solution:
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