Motion in a Straight Line for NEET UG
Motion along a straight line is the starting point of mechanics. Master displacement, velocity, acceleration and the three equations of motion here, and the rest of mechanics gets easier.
PhysicsClass 1176 MCQs3 lessons12 flashcards3 memory tricks
Practise Motion in a Straight Line free
What you'll learn
- Displacement, velocity and acceleration
Tell distance from displacement and speed from velocity, and read motion from position–time and velocity–time graphs. - The three equations of motion
Choose and use the right equation for motion with constant acceleration. - Free fall: motion under gravity
Apply the equations of motion to bodies thrown up or dropped, taking g with the correct sign.
Key formulas
| No s | v = u + at |
|---|---|
| No v | s = ut + ½at² |
| No t | v² = u² + 2as |
| Distance in the nth second | sₙ = u + (a/2)(2n − 1) |
| Maximum height (thrown up at u) | H = u²/2g |
| Time to reach the top | t = u/g |
| Total time of flight | T = 2u/g |
Memory tricks
Slope of an x–t graph is velocity. Slope of a v–t graph is acceleration, and the area under a v–t graph is displacement.
With uniform acceleration from rest, distances covered in the 1st, 2nd, 3rd… second are in the ratio 1 : 3 : 5 : 7 (odd numbers). Total distances after 1, 2, 3 s are 1 : 4 : 9.
Ignoring air resistance, time up = time down = u/g, total flight time = 2u/g, and the ball comes back to your hand with speed u, now downwards. At the top, v = 0 but a = g.
Try 3 NEET-style questions
Q1. A ball is thrown vertically upward with speed u. Neglecting air resistance, its speed when it returns to the point of projection is
- zero
- u/2
- u
- 2u
Show answer
Answer: (3) u
With no air resistance, the motion is symmetric: the ball loses speed going up and regains the same speed coming down, returning with speed u.
Q2. The slope of a velocity–time graph gives
- displacement
- acceleration
- speed
- position
Show answer
Answer: (2) acceleration
Slope of v–t graph = Δv/Δt = acceleration. The area under it gives displacement.
Q3. Two cars move in the same direction with speeds 60 km/h and 40 km/h. The velocity of the first car relative to the second is
- 100 km/h
- 20 km/h
- 50 km/h
- 10 km/h
Show answer
Answer: (2) 20 km/h
v₁₂ = v₁ − v₂ = 60 − 40 = 20 km/h, in the direction of the first car.
Practise all 76 questions Free · explanations for every option · see where you go wrong