By Ben Winegar

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-1. What is the weight of a 3.4 kg mass?

F = ma Weight = force F = 3.4 x 9.8 = 33.32 N

0. What mass has a weight of 720 N?

F = ma 720 = m x 9.8 m = 720/9.8 m =
73.5kg

1. Bob must exert 240 N of force on a 980 Kg car to move it at a constant speed up an incline. (The frictional force is 240 N) What is the acceleration of the car if he exerts a force of 350 N?

F = 350 - 240 = 110 N F = ma 110 = 980 x
a a = 110/980 a = .112 m/s/s

2. What is the acceleration of a 6 Kg object hanging on a string that is under a tension of 80 N? 30 N? (Make up positive)

F = 80 - (9.8 x 6) = 21.2 N F = ma
21.2 = 6 x a a = 21.2/6 a = 3.5 m/s/s

F = 30 - (9.8 x 6) = -28.8 N F = ma -28.8 = 6 x a a = -28.8/6 a = -4.8 m/s/s

3. What force is needed to accelerate a 60 Kg cart and rider from rest to 4.2 m/s in 2.5 seconds when the friction force is 24 N?

a_{av = }Dv/Dt
a_{av } = 4.2/2.5 = 1.68 F = ma
(F - 24) = 60 x 1.68 F = 124.8 N

4. What is the mass of a box that moves at a constant velocity along a surface with a force of 15 N, and accelerates at 4.2 m/s/s when you exert 26 N?
F = ma (26 - 15) = m x 4.2 m =
11/4.2 m = 2.6 kg

5. If you exert a force of 60 N on a car, it moves at a constant velocity. (i.e. there is a frictional force of 60 N) What is its mass if when you exert 80 N on it, it accelerates from rest to 2 m/s in 100 seconds?

a_{av = }Dv/Dt
a_{av }= 2/100 = .02 F =
ma (80 - 60) = m x .02 m =
20/.02 m = 1000 kg

6. A 60 Kg rocket accelerates upward from rest reaching a height of 23.4 m in 3.0 seconds. What must be the thrust of the engine?

s = ut + ^{1}/_{2}at^{2 }
23.4 = (0 x 3) + .5 a 3.0^{2 } 23.4 =
4.5a a = 5.2

F = 60 x 9.8 = 588 (F - 588) = 60 x 5.2 F - 588 = 312 F = 900 N

7. It takes 45 N to make a 10 kg cart move at a constant speed. What force does it take to make the cart accelerate at 3.2 m/s/s in the direction it is moving?

F = ma (F - 45) = 10 x
3.2 F - 45 =
32 F = 77 N

8. What tension would accelerate a 5.0 Kg object suspended on a string upwards at 6.2 m/s/s? Downwards?

F = 5.0 x 9.8 = 49 F = ma (F -
49) = 5.0 x 6.2 F - 49 = 31 F = 80 N

F = ma (F - 49) = 5.0 x -6.2 F - 49 = -31 F = 18 N

9. A 45 gram rocket accelerates upward from 0 to 12 m/s in .05 seconds What must be the thrust of the engines?

a_{av = }Dv/Dt
a_{av } = 12/.05 = 240 F
= .045 x 9.8 = .441 F = ma (F - .441)
= .045 x 240 F = 11.241 N

10. (Hard - Extra credit - won't be on the quiz!) A rocket has engines that produce 60 N of thrust. What is its mass if it accelerates upward at 40 m/s/s?

F = ma (60 - 9.8m) = m x
40 60 =
49.8m m = 1.2 kg