c5-work and energy

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INTAN, HAJA R, AISYAH, AZLINA DEPARTMENT OF APPLIED SCIENCES

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UiTM PULAU PINANGSEMESTER JULAI OKT 2010

PHY130 FUNDAMENTAL PHYSICS IWORK AND ENERGY

PART A

Question 1 A 2000 kg car starts from rest at point A and moves with constant acceleration of 3 m s -2 to point B within 5 s. Find the change of kinetic energy of the car between point A and B.

A. 15, 000 JB. 100, 000 JC. 125, 000 JD. 225, 000 J

Question 2 A 12 kg object is moving on a rough, horizontal surface. It has 24 J of kinetic energy.The friction force acting on it is 0.5 N. How far will it slide?

A. 2 mB. 12 mC. 24 mD. 48 m

Question 3 A constant force of 15 N is applied to an object of mass 5.0 kg at an angle of 35 withthe horizontal. What is the work done by this force on the object if it causes adisplacement of 1.5 m along the horizontal direction?

A. 0 JB. 1.8 JC. 18 JD. 28 J

Question 4 A horizontal force is 2000 N is applied to a vehicle of mass 400 kg which is initially atrest on a horizontal surface. If the total force apposing the motion is constant at 800N,calculate the acceleration of the vehicle.

A. 3 ms -2 B. 4 ms -2 C. 5 ms -2 D. 6 ms 2

Question 5Refer to question no. 4 . Calculate the kinetic energy of the vehicle 5 s after the force isapplied.

A. 20 000 JB. 30 000 JC. 45 000 JD. 50 000 J


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Question 6 A box of mass 5.0 kg is accelerated from rest by a force across along a floor at a rate 2.0ms -2 for 7 s. Find the net work done on the box.

A. 3.5 x 10 2 J B. 4.9 x 10 2 JC. 5.0 x 10 2 JD. 6.6 x 10 2 J

Question 7In which one of the following situations is zero net work done?

A. A ball rolls down an inclined plane.B. A physics student stretches a spring.C. A box is pulled across a rough floor at constant velocity.D. A child pulls a wagon across a rough surface causing it to accelerate.

Question 8The rate at which work is done is equivalent to which of the following?

A. increase in potential energy

B. thermal energyC. potential energyD. power

Question 9 A stationary truck is pushed using a force of 2F. If the truck remains stationary, what isthe work done by the truck?

A. 2FB. F/2C. remains constant but non-zero.D. remains constant at zero.

Question 10 A 50-kg elevator is pulled upward with a constant force of 550 N for a distance of 5.0m.What is the work done by the 550 N force?

A. 2.75 x10 3JB. -2.45 x 10 3JC. 3.00 x10 4JD. -5.20 x 10 5J

Question 11What is represented by the area under the curve of a force versus time (f vs. t) graph?

A. impulseB. momentum

C. workD. kinetic energy


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Question 12 A horizontal force P pulls a 10 kg mass across the floor at a constant speed as shown inFigure 2.The coefficient of kinetic friction is 0.50. Calculate the work done by the force Pin moving the 10 kg mass through a distance of 4 m.

A. 146JB. 196JC. 255JD. 392J

Question 13 A 500 kg elevator is pulled upward with a constant force of 5500 N for a distance of 50.0m. What is the work done by the 5500 N force?

A. 2.75 x10 5JB. -2.45 x10 5JC. 3.00 x10 4J

D. -5.20 x105

J

Question 14When is kinetic energy conserved?

A. in elastic collisionsB. in inelastic collisionsC. in any collision in which the objects do not stick togetherD. in all collisions

Question 15In which one of the following situations is zero net work done?

A. A ball rolls down an inclined plane.B. A physics student stretches a spring.C. A child pulls a wagon across a rough surface causing it to accelerate.D. A box is pulled across a rough floor at constant velocity.

Question 16 A physics student pushes a 0.50 kg block from the bottom of a frictionless 30.0 inclinedplane as shown in Figure 2.0. The student performs 4.0 J of work and the block slides adistance s along the incline before it stops. Determine the value of s.

A. 16 cmB. 82 cmC. 160 cmD. 330 cm


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PART B

QUESTION 1a) At Sunway Lagoon Theme Park, a man of mass 60 kg enters the final section of awaterslide at a speed of 5.0 m/s as shown in Figure 7. The final section is 5.5 m highand 5.0 m long. The frictional force between the man and the waterslide is 10 N. Find:i) the change in potential energy when he arrives at the bottom of the waterslide.

(2 marks)ii) the work done by friction. (2 marks)iii) the man's velocity at the bottom of the waterslide. (3 marks)

b) A force of 6.0 N acts on an object through a distance of 15 m in the opposite directionof the motion. Find the work done on the object. (3 marks)

QUESTION 2a) Find the tensions T 1 and T 2 of the cord if the weight of the suspended object is 60 Nas shown in Figure 4. (7 marks)

b) A man pushes a trolley through a horizontal distance of 5.0 m with a force of 25 N atan angle of 30 from the vertical. What is the work done by the man? (2 marks)

c) A bullet of mass 20 g, initially moving with a velocity of 400 ms"1 embedded into awooden block. What is the average retarding force on the bullet? (3 marks)


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QUESTION 3a) A car of mass m moving with a velocity u collides with another car of the same massthat is stationary. After collision, the two cars stick and move with a common velocity v.Calculate in terms of m, u and vi) The common velocity, v. (2 marks)ii) The total kinetic energy before collision. (2 marks)iii) The total kinetic energy after collision. (2 marks)iv) The loss of kinetic energy. (2 marks)

b) A 10.0kg crate slides along a horizontal frictionless surface at a constant speed of4.0m/s. The crate then slides down a frictionless incline and across a second horizontalsurface as shown in Figure 6.

i) What is the kinetic energy of the crate as it slides on the upper surface?ii) What is the speed of the crate when it arrives at the lower surface?iii) What is the work done by friction on the crate as it slides to a stop on the lowersurface?iv) What minimum coefficient of kinetic friction is required to bring the crate to a stop overa distance of 5.0 m along the lower surface?

(9 marks)

QUESTION 4

a) A uniform plank of length 2.00 m and mass 30.0 kg is supported by three ropes, T 1, T 2 and T 3 as shown in Figure 6.0. A 700 N person stands at 0.500 m from the left end.i) Draw all the forces acting on the system.ii) If the system is in equilibrium, determine the tension in ropes, T 2 and T 3.

(6 marks)

b) A baseball pitcher throws a fastball that leaves his hand at a speed of 36.0 m/s. Themass of the baseball is 0.145 kg. Ignore air resistance. How much work has the pitcherdone on the ball in throwing it?

c5-work and energy

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