NJC Motion and Forces Problem Set 2025

National Junior College Science Department | Physics 3. Motion and Forces Problem Set 3.1 KINEMATICS 3.1.1 Exercises For this section of the problem set, you should try the exercises without looking at the solutions. The solutions are there if you get stuck and you should also use it to understand how to present your work. E1 Distinguish whether the following statements describe speed, velocity, distance, or displacement. (a) The ship sailed south-west for 200 km. (b) I averaged 11 km h−1 during the marathon. (c) The snail crawled at 2 mm s−1 along the straight edge of a bench. (d) The sales representative’s round trip was 420 km. E2 Explain whether the speedometer of a car registers its speed or velocity. E3 A student walks 3.0 km due north, and then 4.0 km due east. By drawing a vector diagram showing the route, calculate (a) the total distance travelled, [7.0 km] (b) the displacement of the student. [5.0 km at 53° east of north] E4 A sprinter, starting from blocks, reaches his full speed of 9.0 m s −1 in 1.5 s. Determine the sprinter’s average acceleration. [6.0 m s−2] E5 A railway train, travelling along a straight track, takes 1.5 minutes to come to rest from a speed of 115 km h−1. Determine the average acceleration of the train. [−0.35 m s−2] E6 The Earth takes one year to orbit in a circle around the Sun at a distance of 1.5 × 10 11 m. Calculate the average speed and average velocity of the Earth over one year. [30 000 m s−1, 0 m s−1] E7 A racing car accelerates for 10 s through three gear changes with the following average speeds: 20 m s−1 for 2.0 s 40 m s−1 for 2.0 s 60 m s−1 for 6.0 s Determine the average speed of the car during the 10 s acceleration. [48 m s−1]

National Junior College Science Department | Physics 3.1.2 Practice P1 A student walks 8.0 km south-east and then 10 km due west. (a) Draw a vector diagram showing the route. (b) Calculate, using trigonometry, the displacement of the student. P2 A railway train travels at a constant speed of 60 km h −1. It moves e ast for 40 min, then 45° west of north for 30 min. Determine the average velocity of the train. 3.2 DESCRIBING MOTION WITH GRAPHS 3.2.1 Exercises E8 The displacement of a racing car at different times as it travels along a straight track during a time trial is shown below. displacement / m 0 85 170 255 340 time / s 0 1.0 2.0 3.0 4.0 (a) Draw a displacement-time graph for this motion. (b) Determine the velocity of the car. [85 m s−1] E9 The velocity of a motorcyclist at different times as it travels along a straight road during a time trial is shown below. velocity / m s−1 0 15 30 30 20 10 0 time / s 0 5 10 15 20 25 30 (a) Draw a velocity-time graph for this motion. (b) Determine the motorcyclist’s acceleration during the first 10 s. [3.0 m s−2] (c) Determine the motorcyclist’s acceleration during the last 15 s. [−2.0