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 $\frac{5}{2} \frac{m}{s}$ $5/2 m/s$ ?

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Answer 1 · 2017-05-18T12:23:13

The time is $= 0.6 s$ $=0.6s$

Voltage is $U = 7 V$ $U=7V$

Current is $I = 3 A$ $I=3A$

The power of the motor is

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

Velocity is $v = \frac{5}{2} m s^{- 1}$ $v=5/2ms^-1$

Mass is $m = 4 k g$ $m=4kg$

The kinetic energy of the car is

$K E = \frac{1}{2} m v^{2} = \frac{1}{2} \cdot 4 \cdot {(\frac{5}{2})}^{2} = \frac{25}{2} J$ $KE=1/2mv^2=1/2*4*(5/2)^2=25/2J$

But,

$E = P \cdot t$ $E=P*t$

The time is $t = \frac{\frac{25}{2}}{21} = 0.6 s$ $t=(25/2)/21=0.6s$

An electric toy car with a mass of 4kg4 kg is powered by a motor with a voltage of 7V7 V and a current supply of 3A3 A. How long will it take for the toy car to accelerate from rest to 52ms5/2 m/s?