A cargo train pulls wagons along a straight, level track. The locomotive driver increases the driving force from 60 000 N to 75 000 N while the train is alr...
Question 1 Report
A cargo train pulls wagons along a straight, level track. The locomotive driver increases the driving force from 60 000 N to 75 000 N while the train is already moving. At that instant, the total resistive force from air and rolling friction is 60 000 N. The train has a mass of 300 000 kg. The railway company uses these values to decide when the train can safely reach a new speed limit. The wheels rotate about their axles rather than a pivot, and no nuclear energy source is involved.
(a) Calculate the resultant force on the train just after the driving force is increased. [2]
(b) Use the equation F = ma to calculate the acceleration of the train. [3]
(c) Explain why the acceleration becomes smaller as the train's velocity rises. [2]
Answer Details
- (a) Resultant force is driving force minus resistive force:
\[75000\text{ N}-60000\text{ N}=15000\text{ N}\]
The resultant force is 15 000 N forwards. [2] - (b) Use \(F=ma\), rearranged to \(a=F/m\):
\[a=\frac{15000\text{ N}}{300000\text{ kg}}=0.050\text{ m s}^{-2}\]
The acceleration is 0.050 m s−2. [3] - (c) As velocity rises, air resistance increases. This reduces the forward resultant force, and since \(a=F/m\), the acceleration decreases. [2]
Download The App On Google Playstore
Everything you need to excel in your exams
