An express train is moving with a velocity v1. Its driver finds another train is moving on the same track in the same direction with velocity v2. To escape collision, driver applies a retardation a on the train. the minimum time of escaping collision will be [RPET 2002]

• A.                \[t=\frac{{{v}_{1}}-{{v}_{2}}}{a}\]                 
• B.                           \[{{t}_{1}}=\frac{v_{1}^{2}-v_{2}^{2}}{2}\]         
• C.                None                                
• D.                Both