Rankers Physics
Topic: Kinematics
Subtopic: Equations of Motion

Two cars A and B are approaching each other head-on with speeds 20 m/s and 10 m/s respectively. When their separation is X then A and B start braking at 4 m/s² and 2m/s² respectively. Minimum value of X to avoid collision is
60 m
75 m
80 m
90 m

Solution:

Using the stopping distance formula:

 

s=u22as = \frac{u^2}{2a}

 

For Car A (

uA=20u_A = 20

m/s,

aA=4a_A = 4

m/s²):

 

sA=2022×4=4008=50 ms_A = \frac{20^2}{2 \times 4} = \frac{400}{8} = 50 \text{ m}

 

For Car B (

uB=10u_B = 10

m/s,

aB=2a_B = 2

m/s²):

 

sB=1022×2=1004=25 ms_B = \frac{10^2}{2 \times 2} = \frac{100}{4} = 25 \text{ m}

 

Total minimum separation to avoid collision:

 

X=sA+sB=50+25=75 mX = s_A + s_B = 50 + 25 = 75 \text{ m}

 

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