關於dynamics既物理問題

Tieria

2010-10-02 2:30 am

1. An elevator is descending with an acceleration of 3 ms-2. A student inside performs an experiment on free fall in order to determine the acceleration due to gravity. He uses an object of mass 2 kg.(a) What would his result be?(b) He then checks the result by weighing the object on a bathroom scale inside the elevator. What would be the reading as shown on the bathroom scale? 2. An astronaut of mass 75 kg is in a spaceship during take-off. The spaceship is accelerating upwards at 20ms-2. Find the force acting on the astronaut by the seat.3. A light string passes over a fixed pulley of negligible mass and friction. Two masses of M = 3kg and m = 2kg are hung separately at the two ends of the string.(a) Find the acceleration of the masses.(b) Find the vertical downward force acting on the pulley. ※ 請列明計算步驟。※

回答 (1)

天同

2010-10-02 6:04 am

✔ 最佳答案

1. (a) Let g' be the experimental result of g, i.e. the apparent acceleration due to gravity
Since the elevator is accelerating downward, the acceleration of the object during free fall inside the elevator with respect to the elevator itself is (g - 3) m/s2
hence, g' = (g - 3) m/s2 = (10 - 3) m/s2 = 7 m/s2.
where g is the true acceleration due to gravity, taken to be 10 m/s2 for simplicity

(b) The reading on the scale = 2 x 7 N = 14 N
2. Let F be the force acting on the astronautF - 75g = 75 x 20
hence, F = (75x20 + 75 x 10) N = 2250 N

3. (a) Net force acting on the masses = (3 - 2)g N = g N = 10 N
hence, acceleration = 10/(3+2) m/s^2 = 2 m/s^2

(b) Let T be the tension on the string. Consider the 2 kg mass,T - 2g = 2 x 2
i.e. T = (4 + 2g) N = 24 N
Hence, vertical downward force acting on the pulley= 2 x 24 N = 48 N

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