9th Class Science Time and Motion Question Bank Motion HOTS Subjective Problems

  • question_answer
    The acceleration of a car started at t - 0, varies with time as shown in figure. What is the distance travelled in 30 seconds?

    Answer:

    Given a-t graph: 
    (i) Between 0 to 10s, a is constant, i.e., \[5ft/{{s}^{2}}.\] \[{{t}_{2}}=?\]In the first 10s, distance covered, \[{{S}_{1}}=ut6+\frac{1}{2}a{{t}^{2}}=0+\frac{1}{2}\times 5\times {{10}^{2}}=250ft\]c At 10s, velocity acquired,\[\Rightarrow \] \[=0+5\times 10=50m/s\] (ii) Between 10s to 20s [i.e.,\[\Delta t=20-10=10s]\]it moves with uniform velocity of 50 ft/sec. (\[{{t}_{2}}=10\,\sec \]acceleration is zero) \[\therefore \] Distance covered,\[{{S}_{2}}=50\times 10=500ft.\] (iii) Between 20s to 30s, acceleration is constant i.e., \[-5ft/{{s}^{2}}.\] At 20s, velocity is \[50ft/s;\,\,t=30-20=10s.\] \[\therefore \]Distance covered, \[{{S}_{3}}=ut+\frac{1}{2}a{{t}^{2}}\] \[=50\times 10+\frac{1}{2}(-5){{(10)}^{2}}=500-250=250ft\] \[\therefore \]Total distance travelled in 30s \[=250+500+250=1000ft.\]


You need to login to perform this action.
You will be redirected in 3 sec spinner