Physics

Problem

A car of mass

1200\,\text{kg}

moves on a horizontal road. a. (i) The speed of the car increases uniformly from

10\,\text{m\,s}^{-1}

25\,\text{m\,s}^{-1}

5.0\,\text{s}

. Calculate the average force developed by the engine during this interval, neglecting resistive forces. b. (ii) Observations show that the actual speed variation is better represented by

v(t)=10+3t-0.20t^{2}

(in

\text{m\,s}^{-1}

) for

0\le t\le5\,\text{s}

. Determine the instantaneous force acting on the car at

t=3.0\,\text{s}

. c. (iii) Compare the numerical values obtained in parts (i) and (ii) and state briefly why instantaneous force can differ from average force in an accelerated motion.

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