An electric toy car with a mass of $4 k g$ $4 kg$ is powered by a motor with a voltage of $7 V$ $7 V$ and a current supply of $3 A$ $3 A$ . How long will it take for the toy car to accelerate from rest to $\frac{7}{2} \frac{m}{s}$ $7/2 m/s$ ?

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Answer 1 · 2017-08-14T15:32:10

The time is $= 1.17 s$ $=1.17s$

The power is

$P = U I$ $P=UI$

The voltage is $U = 7 V$ $U=7V$

The current is $I = 3 A$ $I=3A$

The power is

$P = U I = 7 \cdot 3 = 21 W$ $P=UI=7*3=21W$

The kinetic energy of the car is

$E = \frac{1}{2} m v^{2}$ $E=1/2mv^2$

The mass is $m = 4 k g$ $m=4kg$

The speed is $v = \frac{7}{2} m s^{- 1}$ $v=7/2ms^-1$

so,

$E = \frac{1}{2} \cdot 4 \cdot {(\frac{7}{2})}^{2} = \frac{49}{2} J$ $E=1/2*4*(7/2)^2=49/2J$

Let the time $= t s$ $=ts$

$E = P t$ $E=Pt$

$t = \frac{E}{P} = \frac{\frac{49}{2}}{21} = 1.17 s$ $t=E/P=(49/2)/21=1.17s$

An electric toy car with a mass of 4 kg4kg4 kg is powered by a motor with a voltage of 7 V7V7 V and a current supply of 3 A3A3 A. How long will it take for the toy car to accelerate from rest to 7/2 m/s72ms7/2 m/s?