# Grade 12 Physics Questions. HELP?

4. A Klingon space ship is approaching earth at a about 80% of the speed of light (0.8 c) measured relative to earth. It shines a laser beam forward directly through your physics classroom window. The speed this laser as measured by you should be about:

A)1.8c

B)1c

C)0.9c

D)0.8c

E)0.2c

5. Isaac Newton shot a dirty snowball 76m across a horizontal field. It passed directly over Edmund Hailey's head, and was in the air for 7.6s. How high did it get above the field? Answer in m.

A)18

B)51

C)71

D)160

E)0.2C

6. Snoopy is flying his biplane at an altitude of 225m above Lake Ontario, which is 160 m deep. Using his machine gun sights, he sees the Red Baron in a submarine resting on the bottom of the lake. The sights of Snoopy's gun point 37 degrees below horizontal. Whit is horizontal separation between Snoopy and the Red Baron? Answer in m?

A)510

B)460

C)420

D)380

E)290

7. Bill Bennett open Expo '86 by dropping 2 small balls, one 3 times the mass of the other, vertically from a height of 5m above the floor. the heavier ball is just beneath the lighter one but not touching it. If all collisions are elastic and air resistance is neglected, what is the maximum height reached by the lighter ball? Answer in m.

A)2.5

B)5

C)10

D)20

E)40

8. Brian Mulroney is taking a ride above the Ottawa River in a hot air ballon. At the instant he is 10 m above the water and moving straight at a rate of 5 m/s, he accidentially drops a coin. At the same moment Michael Wilson, in a boat 25 m directly upstream from the splash down point, drifts along with the current 4 m/s in a futile attempt to save the falling coin. How far is he from the coin when it hits the water? Answer in meters. (using g-10 m/s^2 will simplify this)

A)20

B)17

C)15

D)12

E)8

10. A computer hack, H, has a mass of 70kg. He stands on the ground holding one end of a rope which passes up and over a pulley on the roof of the computer building, then down to a bucket, B, 20 m above his head. the bucket is loaded with used computer paper so that the total load, including the bucket, is 100kg. The hack hangs on as he is pulled upwards to mett the descending load. With what relative speed does the bucket slam into his head? Answer in m/s.

A) 11.8

B)28

C)5.9

D)14

E)7

13. The elevator is much too slow in a certain Physics building so a certain Physics Professor decides to get to the third floor by using a scaffold chair. The professor has a mass of 70kg and the chair has a mass of 10kg. With what steady force must he pull on the rope to achieve an upward acceleration of 0.50 m/s^2? Answer in Newtons.

A)370

B)410

C)820

D)740

E)390

Full solutions please or explanations! Any help is helpful! Super desperate.

### 1 Answer

- WoodsmanLv 78 years agoFavorite Answer
10. Assuming a simple pulley: Consider that the tension in the rope is the same on either side of the pulley, and that the hack and the box accelerate at the same rate (albeit in opposite directions).

hack: Fnet = ma = 70kg * a = T - mg = T - 70kg * 9.8m/s² = T - 686N

So T = 70a + 686

box: Fnet = ma = 100kg * a = mg - T = 100kg * 9.8m/s² - T = 980N - T

so T = 980 - 100a

Then 70a + 686 = 980 - 100a

170a = 294

a = 1.73 m/s²

They meet when each has traveled 10 m.

v² = u² + 2as = 0 + 2 * 1.73m/s² * 10m = 34.6 m²/s²

v = 5.9 m/s

Note: You could probably also do this as an energy problem: The net change in potential energy is (100-70)kg * 10ft * 9.8m/s² = 2940 J

is equal to the combined KE at impact, or

½ * (100+70)kg * v² = 2940 J

v = 5.9 m/s

quite tidily

11. Assuming a simple pulley and a vertical arrangement:

F = ma = 80kg * (9.8 + 0.5)m/s² = 824 N

(C)