Question

A train whose weight is 16 metric tons, moves at the rate of 72 kmph. After applying brakes it stops in 500 meters. What is the force executed by brakes?

• A. 600 N
• B. 1600 N
• C. 3200 N
• D. 6400 N

Answer 1

Answer: (D)

6400 N

Answer 2

To calculate the force exerted by the brakes, you can use the following formula:
Force (F) = (Mass$\times$Acceleration)
First, convert the speed from km/h to m/s:
Speed in $(\frac{m}{s})=\frac{(\frac{72km}{h})\times(\frac{1000m}{km})}{(\frac{3600s}{h})}=\frac{20m}{s}$
The acceleration (a) can be calculated using the formula:
Acceleration $(a)=\frac{(Change in Velocity)}{(Time)}$
The change in velocity is the initial velocity (0 $\frac{m}{s}$ because the train is stopping) minus the final velocity $(\frac{20m}{s})$.
The time (t) is given as the distance (500 meters) divided by the speed $(\frac{20m}{s})$:
a=\frac{(\frac{0m}{s}-\frac{20m}{s})}{(\frac{500m}{\frac{20m}{s}})}$$=\frac{(\frac{-20m}{s})}{(25s)}=\frac{-0.8m}{s^2}
Now, you can calculate the force (F):
F =(Mass$\times$Acceleration) = (16,000 kg$\times$(-0.8 m/s²)) =-12,800 N
The negative sign indicates that the force is acting in the opposite direction of motion (braking force).
So, the correct answer is: (4) 6400 N