Work, Energy & Power PYQs Set 7 (PDF)

Set 7 of 10 · Questions 181-210 of 294

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Mere Teacher · Previous Year Questions JEE Main Physics · Work, Energy & Power · Set 7 (Q181-210)
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181. $A mass m is attached to a thin wire and whirled in a vertical circle. The wire is most likely to break when [NEET 2019]$ (1) $the wire is horizontal$ (2) $the mass is at the lowest point$ (3) $inclined at an angle of 60^{\circ} from vertical$ (4) $the mass is at the highest point$ 182. $Two masses A and B, each of mass M are fixed together by a massless spring. A force acts on the mass B asshown in figure. If the mass A starts moving away from mass B with acceleration ’ a ’, then the acceleration of mass B will be:$ (1) $\frac{F + Ma}{M}$ (2) $\frac{F - Ma}{M}$ (3) $\frac{Ma - F}{M}$ (4) $\frac{MF}{F + Ma}$ 183. $A body of mass (5 \pm 0. 5) kg is moving with a velocity of (20 \pm 0.4) m s^{- 1} . Its kinetic energy will be$ (1) $(1000 \pm0.14) J$ (2) $(500\pm0.14)J$ (3) $(500 \pm 140) J$ (4) $(1000 \pm 140) J$ 184. $A bob of mass m is suspended at a point O by a light string of length l and left to perform vertical motion (circular) as shown in figure. Initially, by applying horizontal velocity v_{0} at the point ' A ', the string becomes slack when, the bob reaches at the point ' D '. The ratio of the kinetic energy of the bob at the points B and C is .$ (1) $1$ (2) $2$ (3) $4$ (4) $3$ 185. $A bag of sand of mass 9.8 kg is suspended by a rope. A bullet of 200 g travelling with speed 10 m s^{- 1} gets embedded in it, then loss of kinetic energy will be$ (1) $4.9 J$ (2) $9.8 J$ (3) $14.7J$ (4) $19.6 J$ 186. $Potential energy (V) versus distance (x) is given by the graph. Rank various regions as per the magnitudes of the force (F) acting on a particle from high to low.$ (1) $F_{CD} > F_{AB} > F_{BC} > F_{DE}$ (2) $F_{CD} > F_{DE} > F_{AB} > F_{BC}$ (3) $F_{BC} > F_{CD} > F_{DE} > F_{AB}$ (4) $F_{BC} > F_{AB} > F_{DE} > F_{CD}$ 187. $When a rubber-band is stretched by a distance x, it exerts a restoring force of magnitude F = ax + b x^{2} where a and b are constants. The work done in stretching the unstretched rubber-band by L is:$ (1) $a L^{2} + b L^{3}$ (2) $\frac{1}{2} (a L^{2} + b L^{3})$ (3) $\frac{a L ^{2}}{2} + \frac{b L ^{3}}{3}$ (4) $\frac{1}{2} (\frac{a L ^{2}}{2} + \frac{b L ^{3}}{3})$ 188. $A block of mass m is kept on a platform which starts from rest with constant acceleration g /2 upward, as shown in fig. work done by normal reaction on block in time t is:$ (1) $- \frac{m g ^{2} t ^{2}}{8}$ (2) $\frac{m g ^{2} t ^{2}}{8}$ (3) $0$ (4) $\frac{3 m g ^{2} t ^{2}}{8}$ 189. $A mass of 1 kg falls from a height of 1 m and lands on a mass less platform supported by a spring having spring constant 15 Nm^{- 1} as shown in the figure. The maximum compression of the spring is. (acceleration due to gravity = 10 ms^{- 2})$ (1) $2 m$ (2) $2 m$ (3) $(\frac{2}{3}) m$ (4) $3 m$ 190. $In case of vertical circular motion of a particle by a thread of length r if the tension in the thread is zero at an angle 30^{\circ} shown in figure, the velocity at the bottom point (A) of the circular path is (g = gravitational acceleration)$ (1) $\frac{7}{2} gr$ (2) $5 gr$ (3) $4 gr$ (4) $\frac{5}{2} gr$ 191. $Consider a force F = - x i^+ y j^. The work done by this force in moving a particle from point A(1, 0) to B(0, 1) along the line segment is: (All quantities are in SI units)$ (1) $\frac{1}{2}$ (2) $\frac{3}{2}$ (3) $2$ (4) $1$ 192. $A body of mass ' m' connected to a massless and unstretchable string goes in verticle circle of radius ' R'under gravity g . The other end of the string is fixed at the center of circle. If velocity at top of circular path is n gR, where, n ⩾ 1, then ratio of kinetic energy of the body at bottom to that at top of the circle is$ (1) $\frac{n ^{2}}{n ^{2} + 4}$ (2) $\frac{n ^{2} + 4}{n ^{2}}$ (3) $\frac{n + 4}{n}$ (4) $\frac{n}{n + 4}$ 193. $A particles of mass m_{1} moving along the X -axis collides with a stationary particle of mass m_{2} and deviates by an angle 30^{\circ} to the X -axis as shown in the figure. If the percentage change in kinetic energy of the combined system of there two particles reduces by 50 %, then the ratio of the masses \frac{m _{2}}{m _{1}} is$ (1) $8$ (2) $6$ (3) $\frac{8}{7}$ (4) $\frac{1}{6}$ 194. $A block of mass 10 kg, moving in x direction with a constant speed of 10 m s^{- 1}, is subject to a retarding force F = 0.1 x J/m during its travel from x = 20 m to 30 m. Its final KE will be:$ (1) $450 J$ (2) $275 J$ (3) $250 J$ (4) $475 J$ 195. $Given below is the plot of a potential energy function U(x) for a system, in which a particle is in one dimensional motion, while a conservative force F(x) acts on it. Suppose that E_{m ec h} =8J, the incorrect statement for this system is:$ (1) $at x> x_{4}, K.E. is constant throughout the region.$ (2) $at x< x_{1}, K.E. is smallest and the particle is moving at the slowest speed.$ (3) $at x= x_{2}, K.E is greatest and the particle is moving at the fastest speed.$ (4) $at x= x_{3}, K.E.=4J$ 196. $A body of mass 0.5 kg travels on straight line path with velocity v = (3 x^{2} +4) m/s. The net work done by the force during its displacement from x = 0 to x = 2 m is:$ (1) $64 J$ (2) $60 J$ (3) $120 J$ (4) $128 J$ 197. $An explosion blows a rock into three parts. Two parts go off at right angles to each other. These two are, 1 kg first part moving with a velocity of 12 m s^{- 1} and 2 kg second part moving with a velocity 8 m s^{- 1} . If the third part flies off with a velocity of 4 m s^{- 1}, its mass would b$ (1) $7 kg$ (2) $17 kg$ (3) $3 kg$ (4) $5 kg$ 198. $A particle moves in one dimension from rest under the influence of a force that varies with the distance travelled by the particle as shown in the figure. The kinetic energy of the particle after it has travelled 3m is:$ (1) $4 J$ (2) $2.5 J$ (3) $6.5 J$ (4) $5 J$ 199. $A time dependent force F = 6t acts on a particle of mass 1kg. If the particle starts from rest, the work done by the force during the first 1 sec. will be:$ (1) $18 J$ (2) $4.5 J$ (3) $22 J$ (4) $9 J$ 200. $A block is fastened to a horizontal spring. The block is pulled to a distance x = 10 cm from its equilibrium position (at x = 0) on a Motionless surface from rest. The energy of the block at x = 5 cm is 0.25 J. The spring constant of the spring is _______N m^{- 1}$ 201. $To maintain a speed of 80 km h^{- 1} by a bus of mass 500 kg on a plane rough road for 4 km distance, the work done by the engine of the bus will be_____kJ. [The coefficient of friction between tyre of bus and road is 0.04]$ 202. $A body is dropped on ground from a height hi and after hitting the ground, it rebounds to a height h_{2} . If the ratio of velocities of the body just before and after hitting ground is 4, then percentage loss in kinetic energy of the body is \frac{x}{4} . The value of x is_____.$ 203. $A body of mass 1 kg begins to move under the action of a time dependent force F = (t i^+ 3 t^{2} j^) N, where i^and j^are the unit vectors along x and y axis. The power developed by above force, at the time t = 2s, will be _____ W.$ 204. $A 0.4 kg mass takes 8s to reach ground when dropped from a certain height ‘P' above surface of earth. The loss of potential energy in the last second of fall is ____J. [Take g = 10 m/ s^{2}]$ 205. $One end of a straight uniform 1 m long bar is pivoted on horizontal table. It is released from rest when it makes an angle 30^{o} from the horizontal (see figure). Its angular speed when it hits the table is given as n s^{- 1}, where n is an integer. The value of n is$ 206. $A block of mass 5 kg starting from rest pulled up on a smooth incline plane making an angle of 30° with horizontal with an effective acceleration of 1 m s^{- 2} . The power delivered by the puling force at t =10 s from the start is_____W. [Use g = 10 m s^{- 2}] (Calculate the nearest integer value)$ 207. $A uniform chain of length 3 meter and mass 3kg overhangs a smooth table with 2-meter laying on the table. If is the kinetic energy of the chain in joule as it completely slips off the table, then the value of k is \dots\dots\dots (Take g = 10 m / s^{2})$ 208. $A solid cylinder length is suspended symmetrically through two massless strings, as shown in the figure. The distance from the initial rest position, the cylinder should by unbinding the strings to achieve a speed of 4 m s^{- 1}, is.......cm. (take g= 10 m s^{- 2})$ 209. $A closed circular tube of average radius 15 cm, whose inner walls are rough, is kept in vertical plane. A block of mass 1 kg just fit inside the tube. The speed of block is 22 m s^{- 1}, when it is introduced at the top of tube. After completing five oscillations, the block stops at the bottom region of tube. The work done by the tube on the block is________J. (Given g = 10 m s^{- 2}).$ 210. $If the maximum load carried by an elevator is 1400 kg (600 kg-Passengers + 800 kg-elevator), which is moving up with a uniform speed of 3 m s^{- 1} and the frictional force acting on it is 2000 N, then the maximum power used by the motor is_____________kW. (g = 10 m s^{- 2})$