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An electric toy car with a mass of #7 kg# is powered by a motor with a voltage of #3 V# and a current supply of #9 A#. How long will it take for the toy car to accelerate from rest to #14/3 m/s#?

Answer 1

Benjamin Asiedu

#0.202 "s"#

The power input is the product of the voltage and the current.

#P = IV#

#= (3 "V") * (9 "A")#

#= 27 "W"#

The change in kinetic energy for the car is

#Delta "KE" = 1/2 m (v^2 - v_0^2)#

#= 1/2 (7 "kg") ((14/3 "m/s")^2 - (0 "m/s")^2)#

#= 76.2 "J"#

Thus, the time needed is the energy divided by the power.

#t = frac{Delta "KE"}{P}#

#= frac{76.2 "J"}{27 "W"}#

#= 0.202 "s"#

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Answer 2

Sebastian Acosta

( t = \frac{m \cdot v}{F} = \frac{7 , \text{kg} \cdot \frac{14}{3} , \text{m/s}}{3 , \text{V} \cdot 9 , \text{A}} )

( t \approx 0.54 , \text{s} )

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Answer from HIX Tutor

When evaluating a one-sided limit, you need to be careful when a quantity is approaching zero since its sign is different depending on which way it is approaching zero from. Let us look at some examples.