Assume the gravitational acceleration g on the Earth to be 10 ms^-2
1. A ball on the ground is thrown upward with an initial speed of 20 ms^-1. Which statement(s) is (are) correct? I. The highest point that the ball can reach is 40 m above the ground. II. Its speed will always decrease. III. When the ball is 7.2 m above the ground, its speed is 16 ms^-1. IV. The time for the ball to reach the highest point is 2 s. A. I, IV B. II, III. C. III, IV. D. II, III, IV.
2. A moving cart of 40 kg stops after sliding for 5 s on a rough road. The friction acting on it is 400 N. Find its initial speed. A. 5 ms^-1 B. 25 ms^-1 C. 50 ms^-1 D. 250 ms^-1
3. A block of 4 kg placed on a smooth plane of inclination 30°is connected with another of 1 kg bya massless string and a smooth pulley as shown in the figure below. Find the tension in the string and the acceleration of the blocks. A. 8 N, 2 ms^-2. B. 12 N, 2 ms^-2. C. 10.93 N, 4.93 ms^-2. D. 14.93 N, 4.93 ms^-2.
4. A ball of 0.1 kg hits vertically on the ground and bounces back. The ball and the ground contact for 0.01 s. The speeds before and after the contact are both equal to 2 ms^-1. Find theaverage force acting on the ball by the ground. A. 20 N B. 39 N C. 40 N D. 41 N
5. A box is placed on a slope of inclination. The maximum magnitude of the friction acting on the box by the slope is half of that of the normal force acting on the box by the slope. What is themaximum value of allowed such that the box will not slide down? A.0.46°. B. 26.6°. C. 30°.D. 60°.
6. What is the probability of choosing a card from a deck and the card is an even number or a redcard or an ace? A. 5/13 B. 1/2 C. 9/13 D. 19/26
小弟physics很渣,另外解答時請列出步驟,謝. 作者: 拉麵仔 時間: 14/8/2010 07:41 PM 提示: 作者被禁止或刪除 內容自動屏蔽作者: inthomaspy 時間: 16/8/2010 02:21 AM Question 1 Statement 1 - False By v^2 - u^2 = 2as 0^2 - 20^2 = 2*-10*s s = 20m Statement 2 - False During the upward motion, the speed of the ball will gradually decrease from 20 ms^-1 to 0 ms^-1 but when the ball falls down, its speed will increase from 0 ms^-1 NB: speed =/= velocity Statement 3 - True By v^2 - u^2 = 2as LHS = 16^2 - 20^2 = -144 RHS = 2*-10*7.2 = -144 Statement 4 - True By v = u + at 0 = 20 + -10*t t = 2s
Question 3 The technique of dealing with such type of question is to draw the free body diagram in horizontal plane 4*10*sin30 <--- 4kg mass ---> tension tension <--- 1kg mass ---> 1*10 mgsin30 T T mg By Fnet = ma, T - 4*10*sin30 = 4a ...(1) 1*10 - T = 1a ...(2) solving (1) & (2), T = 12, a = -2
Question 4 Take downward direction be positive before impact, u = + 2ms^-1 <<< the motion of the ball is vertically downward after impact, v = - 2ms^-1 <<< the motion of the ball is vertically upward By Ft = mv - mu, average force acted on the ball = F = (mv - mu) / t = (0.1*-2 - 0.1*+2) / 0.01 = -40 the negative sign means when the ball hits the ground, there exist a force acted by the ground on the ball vertically upward
Question 6 In a deck, there are number 2, 4, 6, 8, 10 which are even Hence there are 5 * 4 (number of even numbers * number of cards for each number) cards = 20 cards for even There are 26 cards which are red, but excluding the red cards for even numbers There are 16 cards for red which are not even numbers Finally, there are 4 cards for ace, but 2 cards of ace are red Hence 2 cards for ace which are not red
Required probability = [20(even) + 16(red excluding 'even red' as the 'even red' are counted before) + 2(ace excluding red)] / 52
Question 8 代數問題... I = 10^-4, Io = 10^-12 B = 10 log (10^-4 / 10^-12) = 80 also...answer A, B, D seems not practical... A is too large...B is too small...D is too small too (we seldom hear sound of negative sound intensity level)...
