Ch-2

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Ch-2

• Help-Session

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CH-2-072

• T072 Q2.The position of an object is given as a
  function of time by , x 4t2-3t3 where x is in
  meters and t is in seconds. Its average
  acceleration during the interval from t 1.0 s
  to t 2.0 s is (Ans -19 m/s2)

• Q3. A car starts from rest and undergoes a
  constant acceleration. It travels 5.0 m in the
  time interval from t 0 to t 1.0 s. Find the
  displacement of the car during the time interval
  from t 1.0 s to t 2.0 s.( Ans 15 m)

? x1vitat2/2 vavg (vivf)/2 vf/2?x/?t
vf/2?x/?t5 vf2x510 m/s a vf-vi/t10/110
m/s2 ? x2vtat2/210x110x1/2 105
15 m
vdx/dt8t-9t2 aavg?v/ ?t
v(t2s)-v(t1s)/(2-1) -20-(-1)/1-19 m/s2
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CH-2-072

• Q4. Fig. 1 represents the velocity of a car (v)
  moving on a straight line as a function of time
  (t). Find the acceleration of the car at 6.0 s.
  (A ns -3.0 m/s2)

a ?v/?t(0-12)/(8-4)-12/4 -3m/s2
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CH-2-071
T071  Q3.Fig 1 shows the position-time graph of
an object. What is the average velocity of the
object between t0.0 s and t 5.0 s? (Ans 2.0
m/s)
Q4. Fig 2 shows a velocity-time graph of a
runner. If the runner starts from the origin,
find his position at t 4.0 s.( Ans 45 m)
? x1 area of v-t graph ?x1 (1X10)/2(1x10)
(10x 2) (10x2)/2 xf-xi 510201045
m xf45 m
V ? x/ ? t xf-xi/tf-ti
(10-0)/(5-0) 10/52 m/s
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CH-2-071
Q5.An object is thrown vertically upward with an
initial speed of 25 m/s from the ground. What is
the height of the object 1.0 s before it touches
ground?(Ans20 m)
Q6. A car starts from rest and accelerates at a
rate of 2.0 m/s2 in a straight line until it
reaches a speed of 20 m/s. The car then slows
down at a constant rate of 1.0 m/s2 until it
stops. How much time elapses (total time) from
start to stop? (Ans 30 s)
Velocity at touch down vf-25 m/s Velocity 1s
before vf vivfgt -259.8x1-15.2 m/s
then ?y in last sec(vf2-vi2)/(-2 g) ?y(-15)2
- (-15.2)2/(-2x9.8) ?y(625-231)/(-19.6)-19.99
m yi - 20 m
Total time t1t2 t1vf-vi/a1(20-0)/2 10 s t2
(0-20)/-1 20 s Total time 10 s 20 s 30 s