I.E. IRODOV > Problems in general physics
Problems in General Physics → Physical Fundamentals of Mechanics →
Kinematics
1.1. A motorboat going downstream overcame a raft at a point A; τ = 60 min later it turned back and after some time passed the raft at a distance l = 6.0 km from the point A. Find the flow velocity assuming the duty of the engine to be constant.
1.2. A point traversed half the distance with a velocity v_{0}. The remaining part of the distance was covered with velocity v_{1} for half the time, and with velocity v_{2} for the other half of the time. Find the mean velocity of the point averaged over the whole time of motion.
1.3. A car starts moving rectilinearly, first with acceleration w = 5.0 m/s^{2} (the initial velocity is equal to zero), then uniformly, and finally, decelerating at the same rate w, comes to a stop. The total time of motion equals τ = 25 s. The average velocity during that time is equal to <v> = 72 km per hour. How long does the car move uniformly?
1.4. A point moves rectilinearly in one direction. Fig. 1.1 shows the distance s traversed by the point as a function of the time t. Using the plot find:
1.5. Two particles, 1 and 2, move with constant velocities v_{1} and v_{2}. At the initial moment their radius vectors are equal to r_{1} and r_{2}. How must these four vectors be interrelated for the particles to collide?
1.6. A ship moves along the equator to the east with velocity v_{0} = 30 km/hour. The southeastern wind blows at an angle φ = 60° to the equator with velocity v = 15 km/hour. Find the wind velocity v' relative to the ship and the angle φ' between the equator and the wind direction in the reference frame fixed to the ship.
1.7. Two swimmers leave point A on one bank of the river to reach point B lying right across on the other bank. One of them crosses the river along the straight line AB while the other swims at right angles to the stream and then walks the distance that he has been carried away by the stream to get to point B. What was the velocity u of his walking if both swimmers reached the destination simultaneously? The stream velocity v_{0} = 2.0 km/hour and the velocity v' of each swimmer with respect to water equals 2.5 km per hour.
1.8. Two boats, A and B, move away from a buoy anchored at the middle of a river along the mutually perpendicular straight lines: the boat A along the river, and the boat B across the river. Having moved off an equal distance from the buoy the boats returned. Find the ratio of times of motion of boats τ_{A}/τ_{B} if the velocity of each boat with respect to water is η = 1.2 times greater than the stream velocity.
1.9. A boat moves relative to water with a velocity which is n = 2.0 times less than the river flow velocity. At what angle to the stream direction must the boat move to minimize drifting?
1.10. Two bodies were thrown simultaneously from the same point: one, straight up, and the other, at an angle of θ = 60° to the horizontal. The initial velocity of each body is equal to v_{0} = 25 m/s. Neglecting the air drag, find the distance between the bodies t = 1.70 s later.
1.11. Two particles move in a uniform gravitational field with an acceleration g. At the initial moment the particles were located at one point and moved with velocities v_{1} = 3.0 m/s and v_{2} = 4.0 m/s horizontally in opposite directions. Find the distance between the particles at the moment when their velocity vectors become mutually perpendicular.
1.12. Three points are located at the vertices of an equilateral triangle whose side equals a. They all start moving simultaneously with velocity v constant in modulus, with the first point heading continually for the second, the second for the third, and the third for the first. How soon will the points converge?
1.14. A train of length l = 350 m starts moving rectilinearly with constant acceleration w = 3.0*10^{2} m/s^{2}; t = 30 s after the start the locomotive headlight is switched on (event 1), and τ = 60 s after that event the tail signal light is switched on (event 2). Find the distance between these events in the reference frames fixed to the train and to the Earth. How and at what constant velocity V relative to the Earth must a certain reference frame K move for the two events to occur in it at the same point?
1.15. An elevator car whose floortoceiling distance is equal to 2.7 m starts ascending with constant acceleration 1.2 m/s^{2}; 2.0 s after the start a bolt begins falling from the ceiling of the car. Find:
1.16. Two particles, 1 and 2, move with constant velocities v_{1} and v_{2} along two mutually perpendicular straight lines toward the intersection point O. At the moment t = 0 the particles were located at the distances l_{1} and l_{2} from the point O. How soon will the distance between the particles become the smallest? What is it equal to?
1.17. From point A located on a highway (Fig. 1.2) one has to get by car as soon as possible to point B located in the field at a distance l from the highway. It is known that the car moves in the field η times slower than on the highway. At what distance from point D one must turn off the highway?
1.19. A point traversed half a circle of radius R = 160 cm during time interval τ = 10.0 s. Calculate the following quantities averaged over that time:
1.20. A radius vector of a particle varies with time t as r = at (1  αt), where a is a constant vector and α is a positive factor. Find:
1.21. At the moment t = 0 a particle leaves the origin and moves in the positive direction of the x axis. Its velocity varies with time as v = v_{0} (1  t/τ), where v_{0} is the initial velocity vector whose modulus equals v_{0} = 10.0 cm/s; τ = 5.0 s. Find:
1.22. The velocity of a particle moving in the positive direction of the x axis varies as v = α sqrt(x), where α is a positive constant. Assuming that at the moment t = 0 the particle was located at the point x = 0, find:
1.23. A point moves rectilinearly with deceleration whose modulus depends on the velocity v of the particle as w = a sqrt(v), where a is a positive constant. At the initial moment the velocity of the point is equal to v_{0}. What distance will it traverse before it stops? What time will it take to cover that distance?
1.24. A radius vector of a point A relative to the origin varies with time t as r = ati  bt^{2}j, where a and b are positive constants, and i and j are the unit vectors of the x and y axes. Find:
1.25. A point moves in the plane xy according to the law x = at, y = at (1  αt), where a and α are positive constants, and t is time. Find:
1.26. A point moves in the plane xy according to the law x = a sin ωt, y = a(1  cos ωt), where a and ω are positive constants. Find:
1.27. A particle moves in the plane xy with constant acceleration w directed along the negative y axis. The equation of motion of the particle has the form y = ax  bx^{2}, where a and b are positive constants. Find the velocity of the particle at the origin of coordinates.
1.29. A body is thrown from the surface of the Earth at an angle α to the horizontal with the initial velocity v_{0}. Assuming the air drag to be negligible, find:
1.31. A ball starts falling with zero initial velocity on a smooth inclined plane forming an angle α with the horizontal. Having fallen the distance h, the ball rebounds elastically off the inclined plane. At what distance from the impact point will the ball rebound for the second time?
1.32. A cannon and a target are 5.10 km apart and located at the same level. How soon will the shell launched with the initial velocity 240 m/s reach the target in the absence of air drag?
1.33. A cannon fires successively two shells with velocity v_{0} = 250 m/s; the first at the angle θ_{1} = 60° and the second at the angle θ_{2} = 45° to the horizontal, the azimuth being the same. Neglecting the air drag, find the time interval between firings leading to the collision of the shells.
1.34. A balloon starts rising from the surface of the Earth. The ascension rate is constant and equal to v_{0}. Due to the wind the balloon gathers the horizontal velocity component v_{x} = ay, where a is a constant and y is the height of ascent. Find how the following quantities depend on the height of ascent:
1.35. A particle moves in the plane xy with velocity v = ai + bxj, where i and j are the unit vectors of the x and y axes, and a and b are constants. At the initial moment of time the particle was located at the point x = y = 0. Find:
1.36. A particle A moves in one direction along a given trajectory with a tangential acceleration w_{τ} = aτ, where a is a constant vector coinciding in direction with the x axis (Fig. 1.4), and τ is a unit vector coinciding in direction with the velocity vector at a given point. Find how the velocity of the particle depends on x provided that its velocity is negligible at the point x = 0.
1.37. A point moves along a circle with a velocity v = at, where a = 0.50 m/s^{2}. Find the total acceleration of the point at the moment when it covered the nth (n = 0.10) fraction of the circle after the beginning of motion.
1.38. A point moves with deceleration along the circle of radius R so that at any moment of time its tangential and normal accelerations are equal in moduli. At the initial moment t = 0 the velocity of the point equals v_{0}. Find:
1.39. A point moves along an arc of a circle of radius R. Its velocity depends on the distance covered s as v = a sqrt(s), where a is a constant. Find the angle α between the vector of the total acceleration and the vector of velocity as a function of s.
1.40. A particle moves along an arc of a circle of radius R according to the law l = a sin ωt, where l is the displacement from the initial position measured along the arc, and a and ω are constants. Assuming R = 1.00 m, a = 0.80 m, and ω = 2.00 rad/s, find:
1.41. A point moves in the plane so that its tangential acceleration w_{τ} = a, and its normal acceleration w_{n} = bt^{4}, where a and b are positive constants, and t is time. At the moment t = 0 the point was at rest. Find how the curvature radius R of the point's trajectory and the total acceleration w depend on the distance covered s.
1.42. A particle moves along the plane trajectory y(x) with velocity v whose modulus is constant. Find the acceleration of the particle at the point x = 0 and the curvature radius of the trajectory at that point if the trajectory has the form
1.43. A particle A moves along a circle of radius R = 50 cm so that its radius vector r relative to the point O (Fig. 1.5) rotates with the constant angular velocity ω = 0.40 rad/s. Find the modulus of the velocity of the particle, and the modulus and direction of its total acceleration.
1.44. A wheel rotates around a stationary axis so that the rotation angle φ varies with time as φ = at^{2}, where a = 0.20 rad/s^{2}. Find the total acceleration w of the point A at the rim at the moment t = 2.5 s if the linear velocity of the point A at this moment v = 0.65 m/s.
1.45. A shell acquires the initial velocity v = 320 m/s, having made n = 2.0 turns inside the barrel whose length is equal to l = 2.0 m. Assuming that the shell moves inside the barrel with a uniform acceleration, find the angular velocity of its axial rotation at the moment when the shell escapes the barrel.
1.46. A solid body rotates about a stationary axis according to the law φ = at  bt^{3}, where a = 6.0 rad/s and b = 2.0 rad/s^{3}. Find:
1.47. A solid body starts rotating about a stationary axis with an angular acceleration β = at, where a = 2.0*10^{2} rad/s^{3}. How soon after the beginning of rotation will the total acceleration vector of an arbitrary point of the body form an angle α = 60° with its velocity vector?
1.48. A solid body rotates with deceleration about a stationary axis with an angular deceleration β ∼ sqrt(ω) where ω is its angular velocity. Find the mean angular velocity of the body averaged over the whole time of rotation if at the initial moment of time its angular velocity was equal to ω_{0}.
1.49. A solid body rotates about a stationary axis so that its angular velocity depends on the rotation angle φ as ω = ω_{0}  aφ, where ω_{0} and a are positive constants. At the moment t = 0 the angle φ = 0. Find the time dependence of
1.50. A solid body starts rotating about a stationary axis with an angular acceleration β = β_{0} cos φ, where β_{0} is a constant vector and φ is an angle of rotation from the initial position. Find the angular velocity of the body as a function of the angle φ. Draw the plot of this dependence.
1.51. A rotating disc (Fig. 1.6) moves in the positive direction of the x axis. Find the equation y(x) describing the position of the instantaneous axis of rotation, if at the initial moment the axis C of the disc was located at the point O after which it moved
1.52. A point A is located on the rim of a wheel of radius R = 0.50 m which rolls without slipping along a horizontal surface with velocity v = 1.00 m/s. Find:
1.53. A ball of radius R = 10.0 cm rolls without slipping down an inclined plane so that its center moves with constant acceleration w = 2.50 cm/s^{2}; t = 2.00 s after the beginning of motion its position corresponds to that shown in Fig. 1.7. Find:
1.54. A cylinder rolls without slipping over a horizontal plane. The radius of the cylinder is equal to r. Find the curvature radii of trajectories traced out by the points A and B (see Fig; 1.7).
1.55. Two solid bodies rotate about stationary mutually perpendicular intersecting axes with constant angular velocities ω_{1} = 3.0 rad/s and ω_{2} = 4.0 rad/s. Find the angular velocity and angular acceleration of one body relative to the other.
1.56. A solid body rotates with angular velocity ω = ati + bt^{2}j, where a = 0.50 rad/s^{2}, b = 0.060 rad/s^{3}, and i and j are the unit vectors of the x and y axes. Find:
1.57. A round cone with halfangle α = 30° and the radius of the base R = 5.0 cm rolls uniformly and without slipping over a horizontal plane as shown in Fig. 1.8. The cone apex is hinged at the point O which is on the same level with the point C, the cone base centre. The velocity of point C is v = 10.0 cm/s. Find the moduli of
1.58. A solid body rotates with a constant angular velocity ω_{0} = 0.50 rad/s about a horizontal axis AB. At the moment t = 0 the axis AB starts turning about the vertical with a constant angular acceleration β_{0} = 0.10 rad/s^{2}. Find the angular velocity and angular acceleration of the body after t = 3.5 s.
