A car of mass $$$1800 \mathrm{~kg}$$$ is towing a trailer of mass $$$400 \mathrm{~kg}$$$ along a straight horizontal road. The car and trailer are connected by a light rigid tow-bar. The car is accelerating at $$$1.5 \mathrm{~m} \mathrm{~s}^{-2}$$$. There are constant resistance forces of $$$250 \mathrm{~N}$$$ on the car and $$$100 \mathrm{~N}$$$ on the trailer. Find the power of the engine of the car at the instant when the speed is $$$20 \mathrm{~m} \mathrm{~s}^{-1}$$$. ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................ ........................................................................................................................................................

Mathematics

IGCSE&ALevel

CAIE

Exam No：9709_s20_qp_41 Year：2020 Question No：2(b)

Answer:

$
F-250-100=2200 \times 1.5(F=3650 \mathrm{~N})
$
(M1 for using Newton's second law for the system or for the car using the result from 2(a))
For use of power $=F v$
$73000 \mathrm{~W}$ or $73 \mathrm{~kW}$

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

Answer:

Knowledge points:

Solution:

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