CHAPTER
2 Motion in Straight Line
Sr.
Concept Formulas Other information
No.
1. Position vector ( r ) rA = x1 i + y1 ˆj + z1kˆ Here, rA ( x1, y1 ) and
rB ( x2 , y2 ) are the position
rB = x2 i + y2 ˆj + z2 kˆ
vectors.
Displacement vector
2. Displacement vector ( r ) r = ( x2 – x1 ) iˆ + ( y2 – y1 ) ˆj + ( z2 – z1 ) kˆ
r = r2 – r1
Total distance travelled Δs s = distance travelled
3. Average speed (vavg ) i.e. vavg =
Total time taken Δt t = time taken
s ds ds = short displacement
4. Instantaneous speed (vinst ) vinst. = lim =
t →0 t dt dt = short time interval
Total distance covered
5. Average speed when vavg = Different uniform speeds
Total time
particle moves with s1 + s2 + s3 +.. + sn v1, v2 , v3 ,...vn in different
=
different uniform speeds t1 + t2 + t3 +.. + tn time intervals t1, t2 ,......tn
in different time intervals v1t1 + v2t2 + v3t3 +.. respectively
=
t1 + t2 + t3 +.
If t1 = t2 = t3 = ........... tn then
v1 + v2 + ........ + vn
vavg =
n
NEET (XI) PHYSICS 1
, Sr.
Concept Formulas Other information
No.
d Particle moves a certain
6. Average speed when vavg =
d d d
particle describes equal + + ..... distance d in n equal parts
nv1 nv2 nvn
distances with different with different speeds
For 2 equal distances. v1, v2 , v3 ,......vn
speeds
2v v
vavg = 1 2
v1 + v2
7. Average velocity Net Displacement r rf – ri rf = final position
, vavg = =
Time taken t tf – ti ri = initial position
tf − ti = time interval
8. Velocity in vector form dr d ˆ dx dy ˆ dz ˆ
v= = ( xi + y ˆj + zkˆ) = iˆ + j+ k Velocity can be positive,
dt dt dt dt dt
negative or zero.
= vxiˆ + vy ˆj + vz kˆ
9. Average acceleration Total change in velocity v v = change in velocity
= aav =
Total time taken t t = time interval
dv d
10. Acceleration in vector a= = (vx iˆ + v y ˆj + vz kˆ) dv = change in velocity
dt dt
form
dv dvy dt = time interval
= x iˆ + ˆj + dvz kˆ
dt dt dt
= axiˆ + ay ˆj + az kˆ
dv d 2 r dr ainst = instantaneous
11. Instantaneous a= = As v = dt
acceleration dt dt 2 acceleration
ainst =
dv dv dx
ainst = dx /dt = instantaneous
dt dx dt velocity
dv
ainst =v When v is function of position (x).
dx
Scalar Form Vector Form Here: v = final velocity
12. Equations of motion
v = u + at v = u + at s = displacement
1 2 1 2 u = initial velocity
s = ut + at s = ut + at
2 2 t = time
v 2 = u 2 + 2as v.v = u.u + 2a.s a = acceleration = constant
These are valid only when
acceleration is constant.
NEET (XI) PHYSICS 2
2 Motion in Straight Line
Sr.
Concept Formulas Other information
No.
1. Position vector ( r ) rA = x1 i + y1 ˆj + z1kˆ Here, rA ( x1, y1 ) and
rB ( x2 , y2 ) are the position
rB = x2 i + y2 ˆj + z2 kˆ
vectors.
Displacement vector
2. Displacement vector ( r ) r = ( x2 – x1 ) iˆ + ( y2 – y1 ) ˆj + ( z2 – z1 ) kˆ
r = r2 – r1
Total distance travelled Δs s = distance travelled
3. Average speed (vavg ) i.e. vavg =
Total time taken Δt t = time taken
s ds ds = short displacement
4. Instantaneous speed (vinst ) vinst. = lim =
t →0 t dt dt = short time interval
Total distance covered
5. Average speed when vavg = Different uniform speeds
Total time
particle moves with s1 + s2 + s3 +.. + sn v1, v2 , v3 ,...vn in different
=
different uniform speeds t1 + t2 + t3 +.. + tn time intervals t1, t2 ,......tn
in different time intervals v1t1 + v2t2 + v3t3 +.. respectively
=
t1 + t2 + t3 +.
If t1 = t2 = t3 = ........... tn then
v1 + v2 + ........ + vn
vavg =
n
NEET (XI) PHYSICS 1
, Sr.
Concept Formulas Other information
No.
d Particle moves a certain
6. Average speed when vavg =
d d d
particle describes equal + + ..... distance d in n equal parts
nv1 nv2 nvn
distances with different with different speeds
For 2 equal distances. v1, v2 , v3 ,......vn
speeds
2v v
vavg = 1 2
v1 + v2
7. Average velocity Net Displacement r rf – ri rf = final position
, vavg = =
Time taken t tf – ti ri = initial position
tf − ti = time interval
8. Velocity in vector form dr d ˆ dx dy ˆ dz ˆ
v= = ( xi + y ˆj + zkˆ) = iˆ + j+ k Velocity can be positive,
dt dt dt dt dt
negative or zero.
= vxiˆ + vy ˆj + vz kˆ
9. Average acceleration Total change in velocity v v = change in velocity
= aav =
Total time taken t t = time interval
dv d
10. Acceleration in vector a= = (vx iˆ + v y ˆj + vz kˆ) dv = change in velocity
dt dt
form
dv dvy dt = time interval
= x iˆ + ˆj + dvz kˆ
dt dt dt
= axiˆ + ay ˆj + az kˆ
dv d 2 r dr ainst = instantaneous
11. Instantaneous a= = As v = dt
acceleration dt dt 2 acceleration
ainst =
dv dv dx
ainst = dx /dt = instantaneous
dt dx dt velocity
dv
ainst =v When v is function of position (x).
dx
Scalar Form Vector Form Here: v = final velocity
12. Equations of motion
v = u + at v = u + at s = displacement
1 2 1 2 u = initial velocity
s = ut + at s = ut + at
2 2 t = time
v 2 = u 2 + 2as v.v = u.u + 2a.s a = acceleration = constant
These are valid only when
acceleration is constant.
NEET (XI) PHYSICS 2
