Question

A tractor, starting from a stationary position, drives down the road. It accelerates at 4 m/s2 for 10 seconds, then travels at a steady pace for another 30 seconds. How much distance has it covered since it started driving?​
A. 1,550 m
B. 1,400 m
C. 200 m
D. 1,200 m

Answer 1

Answer:

B. 1400 meters.

Step-by-step explanation:

According to the statement, there are two stages for the motion of the tractor, in which we need to find the travelled distance:

(i) Uniform accelerated motion.

$s_{i} = s_{o,i} +v_{o,i}\cdot t_{i} + \frac{1}{2}\cdot a\cdot t_{i}^{2}$ (1)

$v_{i} = v_{o,i}+a\cdot t_{i}$ (2)

Where:

$s_{o,i}$ - Initial position of the tractor, measured in meters.

$s_{i}$ - Final position of the tractor, measured in meters.

$v_{o,i}$ - Initial velocity of the tractor, measured in meters per second.

$t_{i}$ - Time, measured in seconds.

$a$ - Acceleration, measured in meters per square second.

$v_{i}$ - Final velocity of the tractor, measured in meters per second.

(ii) Uniform motion.

$s_{ii} = s_{i} + v_{i}\cdot t_{ii}$ (3)

Where:

$s_{ii}$ - Final position of the tractor, measured in meters.

$t_{ii}$ - Time, measured in seconds.

The distance covered by the tractor ($\Delta s$), measured in meters, is:

$\Delta s = s_{ii}$ (4)

If we know that $a = 4\,\frac{m}{s^{2}}$, $t_{i} = 10\,s$, $v_{o,i} = 0\,\frac{m}{s}$, $s_{o,i} = 0\,m$ and $t_{ii} = 30\,s$, then distance covered by the tractor is:

By (1) and (2):

$s_{i} = 0\,m + \left(0\,\frac{m}{s} \right)\cdot (10\,s)+ \frac{1}{2}\cdot \left(4\,\frac{m}{s^{2}} \right) \cdot (10\,s)^{2}$

$s_{i} = 200\,m$

$v_{i} = \left(0\,\frac{m}{s} \right)+\left(4\,\frac{m}{s^{2}} \right)\cdot (10\,s)$

$v_{i} = 40\,\frac{m}{s}$

By (3):

$s_{ii} = 200\,m + \left(40\,\frac{m}{s} \right)\cdot (30\,s)$

$s_{ii} = 1400\,m$

By (4):

$\Delta s = 1400\,m$

The correct answer is B.