An electric toy car with a mass of $2 k g$ $2 kg$ is powered by a motor with a voltage of $9 V$ $9 V$ and a current supply of $7 A$ $7 A$ . 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 · 2017-05-20T06:20:39

The time is $= 0.1 s$ $=0.1s$

Voltage is $U = 9 V$ $U=9V$

Current is $I = 7 A$ $I=7A$

The power of the motor is

$P = U I = 9 \cdot 7 = 63 W$ $P=UI=9*7=63W$

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

Mass is $m = 2 k g$ $m=2kg$

The kinetic energy of the car is

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

But,

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

The time is $t = \frac{\frac{25}{4}}{63} = 0.1 s$ $t=(25/4)/63=0.1s$

An electric toy car with a mass of 2kg2 kg is powered by a motor with a voltage of 9V9 V and a current supply of 7A7 A. How long will it take for the toy car to accelerate from rest to 52ms5/2 m/s?