[1][1]

IITians TAPASYA, Pushpanjali Place, Boring Road Crossing, Opp. Alankar Place, Patna-1, Ph.: 0612-3225103 www.iitianstapasya.com

BATCH :. TARGET PHYSICS WORK ENERGY POWER

IITians TAPASYA...IITians creating IITians

DAILY PRACTICE PROBLEM - 51. A motor drives a body along a straight line witha constant force. The power P developed by

the motor must vary with time t as

(A)

Y

P

O Xt

(B)

Y

P

O Xt

(C)

Y

P

O Xt

(D)

Y

P

O Xt

2. A stone is projected at time t = 0 with a speed V0 and an angle with the horizontal in a uniformgravitational field. The rate of work done (P) by the gravitational force plotted against time (t)will be as

(A)

P

O t

(B)

P

O t

(C)

P

O t (D)

P

O t

Q. 3 to 4 related this Fig.A suitcase of mass M is placed on a level conveyor belt at an airport. The coefficient of staticfriction between the suitcase and the conveyor belt is s and the coefficient of kinetic friction is

k , with k s. The conveyor belt moves with constant speed u, and at time t = 0 the suitcaseis placed on the conveyor with speed v = 0. At a time tf , after moving a distance l, the suitcasecatches up with the conveyor belt, and starts to move at speed u with the conveyor belt. Gravityacts downward with acceleration g > 0. Work can depend on ones frame of reference, so besure to answer the following questions in the frame of reference of the airport.

3. How much work does friction do on the suitcase during this period?

(A) 212

Mu (B) 212

Mu (C) Mgl (D) sMgl4. How much work does the force of friction from the suitcase do on the belt during this time

period?(A) kMgl (B) kMgl (C) k fMgut (D) k fMgut

5. The net power of all the forces acting on a particle (P) versus time (t) curve is shown inFig. Work done upon the particle form A to B P

A B

t

(A) increases(B) decreases(C) first increases then decreases(D) first decreases then increases

BATCH :. TARGET PHYSICS WORK ENERGY POWER [2]

IITians TAPASYA, Pushpanjali Place, Boring Road Crossing, Opp. Alankar Place, Patna-1, Ph.: 0612-3225103 www.iitianstapasya.com

6. Massless springs, each with k = 1350 Nm1are attached to the left and right walls as shown inFig. A 1 kg block is initially held against the left-hand spring, compressing the spring by 0.1 m.The block is released to move. The floor is frictionless except for the section AB. Coefficient offriction for AB is 0.3. Find the distance (in cm) from point B where the block finally comes to

rest.

7. The frictional resistance to the motion of a train is always K times the total weight of the engineand coaches. An engine of weight 2W works at constant horsepower throughtout and attains amaximum speed u = 5 m/s when pulling six coaches each of weight W up the incline. Down thesame incline with only four coaches, the engine can attain a maximum speed 2u = 10 m/s.Find the maximum speed (in m/s) of the engine when pulling two coaches on the horizontallevel.

8. A large block of mass M on a smooth inclined plane is connected via a string to a small blockm. which is attached to a relaxed spring of force cosntant k with its other end attached to theground (see Fig.) Which of the following forces do NEGATIVE work as the large block slidesdown the incline?

(A) The tension force on m(B) The gravitational force on m(C) The spring force on m(D) The tension force on M

9. An object has several forces acting on it. One of these forces is F axy , a force in the x-direction whose magnitude depends on the position of the object, with = 2.50 N/m2 . Calcu-late the work done on the object by this force for the following displacements of the object:(a) The object starts at the point x = 2.00 m, y = 3.00 m and moves parallel to the x-axis to

the point x = 2.00 m, y = 3.00 m.(b) The object starts at the point x = 2.00 m, y = 0 and moves in the y-direction to the point

x = 2.00 m, y = 3.00 m(c) The object starts at the origin and moves on the line y = 1.5x to the point x = 2.00 m,

y = 3.00 m.10. An elevator of heigth h moves upward at constant velocity v. Vibrations cause the elevators

light bulb to fall fro its fixture at time t = 0. The buld hits the floor at time t later. Let the mass ofthe bulb be m.(a) Find the initial kinetic energy of the bulb in ground

frame and elevator frame.(b) Find the kinetic energy of the bulb just before it hits

the floor in ground frame and elevator frame.(c) Find the work done by gravity in ground frame and

elevator frame.ANSWER KEY

1. (A) 2. (D) 3. (A) 4. (D) 5. (A)

6. 25 7. 12 8. (B,C,D) 9. 15 J, zero, 10 J

10. (a) 21 02

mv , (b)2

22vm gh gh ,mgh

(c)

2hmg h v ,mghg