Question
Fig. 1.1 shows a box dropped from an aeroplane. The box contains supplies.
A parachute is attached to the box. The parachute is opened when the time is 6.0 s
The graph in Fig. 1.2 shows the vertical speed of the box as it falls.
(a) State and explain what happens to the kinetic energy of the box during the first 6.0 s of its descent
(b) State and explain what happens to the gravitational potential energy of the box during the first 6.0 s
(c) (i) Use the graph in Fig. 1.2 to determine the speed of the object when the object is moving with a constant speed.
speed of the object at constant speed = ………………………………………….. m / s
(ii) State the size of the resultant vertical force on the box when it is falling at a constant speed
(d) Use the graph in Fig. 1.2 to determine the distance travelled by the box during the first 6.0 s.
distance travelled in first 6.0 s = …………………………………………….. m
(e) Without calculation, describe how Fig. 1.2 shows that the deceleration of the box is greater
than the acceleration of the box.
Answer/Explanation
Answer:
(a) (kinetic energy / it) increases
because) speed / velocity (of box) increases OR faster
(b) gravitational potential energy) decreases
because) height (of box) decreases
(c) (i) any indication on graph / in text that horizontal section represents steady speed
10 (m / s)
(ii) (resultant vertical force =) zero OR 0 (N)
(d) distance = area under graph OR ½ × b × h
(distance =) ½ × 6.0 × 45
135 (m)
(e) deceleration (line) is steeper OR higher gradient than acceleration (line)
Question
A student drops a ball from a high window.
a) The mass of the ball is 0.12 kg.
Calculate the weight of the ball.
weight = ……………………………………………. N
b) Fig. 3.1 shows the speed of the ball while it is falling. The points S, T, U, V and W are shown on the graph.
Draw one line from each section of the graph to the correct description of the motion.
One has been drawn for you.
c) Determine the distance fallen by the ball in section U – V of the graph.
distance = ……………………………………………. m
d) State the distance fallen by the ball in section V – W of the graph.
distance = ……………………………………………. m
Answer/Explanation
Answer:
(a) W = m × g in any form
0.12 × 10
(weight =) 1.2 (N)
(b) Line from T-U to decreasing acceleration
Line from U-V to moving with constant speed
(c) (distance travelled =) area under the graph
2 × 20
40 (m)
(d) 20 OR answer = (c) answer ÷ 2