If the distance travelled by a train is 495 km in 4 hours 30 minutes, what is its speed

4. 50x10= 500m/s 5. 52m/s

The answer is 4f======since electrostatic force is given by    we let f be the electrostatic force when  r = 1 m    if we let  denote the electrostatic force when the distance is decreased so that r = 0.5m, then    we established earlier that f = kq₁q₂. therefore    the force will now be 4f.