Physics · Motion In A Straight Line · NEET
No. Speed and velocity tell you HOW FAST an object moves. Acceleration tells you how fast the velocity CHANGES. A car moving at a steady 100 km/h has high speed but zero acceleration, because its velocity is not changing. Acceleration only exists when velocity changes in size or direction.
Yes. If an object moves with constant velocity (same speed and same direction), its velocity does not change, so a = (v - u)/t = 0. A train cruising at 120 km/h in a straight line has zero acceleration. High speed does not mean high acceleration.
Negative acceleration means the acceleration vector points in the negative direction of your chosen axis. If the object is moving in the positive direction, negative acceleration slows it down (this is called retardation or deceleration). But if the object is already moving in the negative direction, negative acceleration speeds it up. So negative does not always mean slowing down - it depends on the direction of velocity.
Acceleration is a vector. It has both magnitude (how much) and direction. Because velocity is a vector, its rate of change is also a vector. In one dimension (a straight line), we show direction with a + or - sign instead of arrows, which is why NEET straight-line problems use signs so carefully.
The SI unit is metre per second squared, written m/s^2. You get it from the formula: velocity is in m/s, and you divide by time in s, so (m/s) / s = m/s^2. It means the velocity changes by that many m/s every second. For example, 5 m/s^2 means velocity increases by 5 m/s each second.
A bullet enters a wooden block with speed u and, after travelling 24 cm inside it, its speed reduces to u/3. Assuming uniform retardation, the further distance it travels before coming to rest is:
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Acceleration is the rate of change of velocity with time, given by a = (v - u)/t, measured in m/s^2.
Average acceleration = change in velocity / time taken = (v - u)/t, where u is initial velocity and v is final velocity.
The SI unit is m/s^2 and the dimensional formula is [M^0 L^1 T^-2].
Not always. Acceleration means velocity is changing. It can mean speeding up, slowing down (retardation), or even just changing direction. Any change in velocity is acceleration.
Yes. At the highest point of a ball thrown up, velocity is zero for an instant, but acceleration equals g (about 9.8 m/s^2 downward) the whole time. This is a common NEET point.
