Question

define acceleration and give its SI unit when the acceleration of a body negative give two examples of situation in which acceleration of the body is negative

Answer 1

In physics, acceleration is the rate of change of velocity of an object with respect to time. The SI unit for acceleration is metre per second squared (m s−2). A car is moving with high velocity (say v1 = 100km/hr toward North) suddenly it's driver notices a dog crossing the road, applies the brake and reduces the velocity of car to zero(v2 = 0) in 10 seconds (t2 - t1 = 10). So v2 -v1 is negative, implies negative acceleration.A ball thrown up in sky with high velocity(say v1 = 10m/s), reach certain height, then stats falling back and reaches the starting point again with same speed but in opposite direction, (so velocity v2 = -10m/s). Here also v2 - v1 is negative, so negative acceleration. It should be noted that the acceleration here is known as ‘g' or acceleration due to gravity.