NJC Unit 3 Motion & Forces Tutorial

18 Unit 3: Motion & Forces Tutorial Questions Solutions to Questions 8 and 18 provided. Definitions of Displacement, Speed, Velocity, Acceleration 1 (a) Can a body have zero velocity and still be accelerating? (b) Can a body move with a constant speed and still be accelerating? (c) Can the direction of the velocity of a body change when its acceleration is constant? (d) Can a body’s speed be increasing as its acceleration decreases? 2 A trolley is attached to a ticker tape and a timer. As the trolley moves, the timer makes a series of dots on the tape at regular time intervals, usually 1/50 s (i.e. 0.02 s). Figs. (i) to (iv) shows four ticker-tapes. Describe the motion of the trolley which produced them. 3 A stone is dropped off a cliff. When the stone has fallen 4.0 m, a second stone is dropped. Neglecting air resistance as the two stones continue to fall, which of the following statements is/are true? A The velocity of the first stone increases faster than the velocity of the second. B The velocities of both stones increases at the same rate. C The separation of the two stones remains constant throughout the fall. D The separation of the two stones increases as they continue to fall. Graphical Representations of Motion 4 This question is about the motion of a Formula 1 racing car. The graph below shows the velocity of a racing car in the first 4 seconds of a race as it accelerates and slows down to go around the first bend.

19 (a) Using information from Fig. 1, determine [i] the acceleration from t = 0 to t = 2.5 s, [ii] the acceleration from t = 2.5 to t = 3.0 s, [iii] the displacement from t = 0 to t = 2.5 s, [iv] the displacement from t = 2.5 to t = 3.0 s, [v] the displacement from t = 3.0 to t = 4.0 s (b) Calculate the average velocity of the car during the first 4 seconds. (c) Sketch the corresponding acceleration-time graph and displacement-time graph in the figures below. [32 m s-2, -80 m s-2, 100 m, 30 m, 40 m, 42.5 ms-1] Fig. 1

20 5 Figure shows graphs of velocity v against time t for two cars A and B travelling along a straight level road in the same direction. At time t = 0, both cars are side-by-side. (a) Describe the motion of car A from t = 0 to t =10 s. (b) State the time at which both cars have the same velocity. (c) Determine the time at which car A overtakes car B. Explain your method. [1.2 s, 2.4 s] 6 STOPPING DISTANCE PROBLEM A driver travelling in a car on a straight level road sees an obstacle in the road ahead and immediately applies the brakes until the car stops. The initial sp