Initial velocity of motor car, u=7m∕s Stopping distance s=10m Final velocity, v=0m∕s If retardation of car is am∕s2, due to applying brakes, then a=‌
v2−u2
2s
=‌
02−72
2×10
=‌
−4.9
2
m∕s2 Negative sign indicates that retardation is applied in opposite direction of motion. ∴‌ Resistance, ‌R=ma=‌