GS5. Which of the following is a greenhouse gas? University Of Sindh mcqs test

 

WORK POWER AND ENERGY

 (PROBLEMS)

Problem 7.1. Calculate the work done by a force F specified by F = 3i + 4j + 5k in displacing a body from position B to position A along a straight path. The position vectors A & B are respectively given as rA = 2i + 5j — 2k & rB = 7i+ 3j — 5k.

Problem 7.2. A 2000 kg car traveling at 20 m/s comes to rest on a level ground in a distance of 100 m. How large is the average frictional force tending to stop it?

Problem 7.3. A 100-kg man is in a car traveling at 20 m/s. (a) Find his kinetic energy. (b) The car strikes a concrete wall and comes to rest after the front of the car has collapsed 1 m. The man is wearing a seat bell and harness. What is the average force exerted by the belt and harness during the crash?

Problem 7.4. When an object is thrown upward, it rises to a height ‘h’. How high is the object, in terms of h, when it has lost one-third of its original kinetic energy?

Problem 7.5. A pump is needed to lift water through a height of 2.5 m at the rate of 500 g/min. What must the minimum horse power of the pump be?

Problem 7.6. A horse pulls a cart horizontally with a force of 40 Ib at an angle 30° above the horizontal and moves along at a speed of 6.0 miles/hr. (a) How much work does the horse do in 10 minutes? (b) What is the power out put of the horse?

Problem 7.7. A body of mass ‘m’ accelerates uniformly from rest to a speed Vy in time ty. Show that the work done on the body as a function of time ‘t’, in terms of Vy and ty, is 1/2m(Vf2/tf2)t2

Problem 7.8. A rocket of mass 0.200 kg is launched from rest. It reaches a point p lying at a height 30.0 m above the surface of the earth from the starting point. In the process + 425 J of work is done on the rocket by the burning chemical propellant. Ignoring air-resistance and the amount of mass lost due to the burning propellant, find the speed Vy of the rocket at the point P.