Tuesday, 16 September 2014

Work, energy and power numericals class 9th


                                                      "Om Sai Ram"

1. A hammer of mass 1kg falls freely from a height of 2 m .Calculate (I) The velocity and (II) The k.E Of the hammer just before it touches the ground. Does the velocity of hammer depend on the mass of hammer?
2. Calculate the energy posses by a stone of mass 10kg kept at a height of 5m If 196x102 J of energy were used to raise a 40kg boy above the ground, how high would he be raised?
3. Calculate the change that should be affected in the velocity of a body to maintain the same KE , if mass of the body is increased to 4 times.
4. A machine does 192 J of work in 240Sec. What is the power of the machine?
5. A weighting 50kg runs up a hill rising himself vertically 10m in 20Sec. Calculate power. given g=9.8m/s
6. A rickshaw puller pulls the rickshaw by applying a force of 100 N. If the ricksaw moves with constant velocity of 36 kmh-1. Find the power of rickshaw puller.
7. A athlete weighing 60kg runs up a staircase having 10 steps each of 1m in 30 sec. Calculate power (g=9.8m/s)
8. The heart does 1.5 J of work in each heartbeat. How many times per minute does it beat if its power is 2watt
9. Calculate the time taken 60 w bulb to consume 3000 J of energy .
10. A horse exert a force of 200N to pull the cart. If the horse cart system moves with velocity 36kmh-1 on the level road., then find the power of horse in term of horse power .
11. An electric kettle of 500W is used to heat water everyday for 2 hours . Calculate the number of unit of electrical energy consumed y it in 10 days.
12. Calculate the cost of using a 2kwh immersion rod for heating water in a house for one hour each day for 60 days if the rate is Rs. 1.50 per unit kWh.
13. How many unit of energy will be consume by a 100 W refrigerator in 30 days , if it works for 16 hrs. Every day.
14. A 1000w oven is used everyday for 90 min. Calculate the unit of electrical energy oven consume in 30days.
15. The power of a heart which beats 72 times in a minute is 1.2kW. Calculate the work done by heart for each beat.

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