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Sir,will u please give extra more questions based on chapter motion
  1. A train travelling with a velocity of 72 km per hour comes to rest in 40s after the brake is applied. What is the acceleration of the train? What is the retardation ?

 Answer : 

u = 72 km/h

                    = (72 x 5/18)

                    = 20 m/s

v = 0; t = 40 s

           v = u +at

            0 = 20 + a x 40

                = 20 + 40 a

         -20 =  40a or 40a = -20

Therefore a = -20/40 

                      = -1/2  m/s2

Retardation = -a 

                      = +1/2  m/s2

 2.  A train travels 40 km at a uniform speed of 30 km/hr. Its average speed after travelling another 40 km is 45 km/hr for the whole journey. It’s speed in the second half of the journey is?

 Ans: Suppose speed of the train in second half be v km/hr; Total distance travelled by the train = 80 km

 

Thus the speed to travel second half  = 90 km/hr

3.   A police jeep is chasing velocity of 45 km/h. A thief in another jeep moving with a velocity of 153 km/h. police fires a bullet with muzzle velocity of 180 m/s the velocity it will strike the car of the thief is?

Ans: Given: Velocity of police jeep = 45 m/hr  = 12.5 m/s 

Velocity of thief’s jeep  = 153 km/hr = 42.5 m/s

Velocity of bullet  = 180 m/s

Now, since bullet is fired from police jeep which is going at 42.5 m/s,

Therefore, velocity of bullet is (180 + 12.5) = 192. 5 m/s.

To calculate velocity with which bullet with hit the thief we use concept of relative velocity.

Therefore, we have VBT  = VB - VT Here VB is velocity of bullet and  VT is velocity of thief

VBT = 192. 5m/s  -  42.5 m/s  = 150m/s

4.  A car moves with a speed of 30 km/h for half an hour; 25 km/h for 1 hr and 40 km/hr for 2 hrs. Find average speed.

Ans: Distance travelled with a speed of 30 km/h for half an hour= 30km/h × 1/2hr = 15 km

Distance travelled with a speed of 25 km/h for an hour = 25 km/h × 1hr  = 25km

Distance travelled with a speed of 40 km / h for 2 hour = 40 km/h × 2hr = 80km

 


5. If a travels first 4okm at speed of 20 km/h and next 80 km at a speed of 40 km/h. What is the average speed of cat during journey?


6.On a 120 km long track, a train travels the first 30 km at a speed of 30 km/h. How fast train travel the next 90 km so that average speed would be 60 km/h?

Ans. Let train travel the next 90 km at speed x km/h, Average speed given = 60 km/h

7.An object covers half the distance with the speed of 20m/s and other half with a speed of 30m/s. Find average speed?

Ans: Let S be the total distance travelled by the object.

It covers (s/2) with speed 30 m/s. Time taken to cover this (S/2) 9s = (S/2) 30 = S/60

Average speed  = Total distance/total time  = (S/2 + s/2) / (S/40 + S/60)  = 24 m/s.

8 .  A car s travelling at 20 m/s along a road. A child runs out into the road 50 m ahead and the car driver steps on the brake pedal. What must the car’s deceleration be if the car is to stop just before it reaches the child?

Answer :

Acceleration = -4 m/s2 or, retardation  = 4 m/s2

 


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