A person is sitting in a car which is at rest. The reaction from the road at each of the four wheels of the car is $R$. When the car runs on a straight level road, how will the reaction at either of the front wheels vary?

When a car accelerates forward on a straight level road, there is a phenomenon called dynamic weight transfer. Due to the inertia of the car's mass and the acceleration force acting at the wheels (below the center of mass), the car tends to "pitch back" or "squat" at the rear. This effectively transfers some of the load from the front wheels to the rear wheels. Analysis of options: A) It will be greater than R: This is incorrect. Weight is transferred away from the front wheels, not towards them. B) It will be less than R: This is correct. The transfer of weight to the rear reduces the normal force (and thus the reaction) on the front wheels. C) It will be equal to R: This would only be true if there were no acceleration or deceleration, or if the acceleration had no effect on weight distribution, which is not the case. D) It shall depend on the material of the road: While the road material affects the maximum friction available for acceleration, the principle of dynamic weight transfer itself due to acceleration is a fundamental mechanical effect and does not depend on the specific material of the road. The question asks how the reaction will vary *when the car runs*, implying it is accelerating. Therefore, when the car accelerates, the reaction at the front wheels decreases.