Just took my opted exam

[thanotoriousfob]

I had questions regarding some of the physics problems on the OPTED exam. If anyone can help show me how to get the answer given that would be great! my real OAT is tomorrow!

11.) A small girl applies a horizontal force of 2 Newtons to a 10- Newton box which slides across the floor with a constant speed of 3 m/s. What is the frictional force, in Newtons, by the floor on the box. The answer is 2.

13.) Atmospheric pressure is very nearly 100kPa. A sealed container of air at 1 atmospheric pressure has a door 1 m wide and 2 m high. This door is very hard to open during HIGH pressure days. If the atmospheric pressure on the outside of the contain is just 1 percent greater than on the inside, then what added force in Newtons is required to open the container door? The answer is 2,000.

16.) A ball is thrown horizontally at 20 m/s from the top of a building and strikes the level ground 50m from the building. Approximately how many meters high is the roof of the building? The answer is 31 m.

22.) If an 80-cm long spring requires 10 Newtons to stretch 5 cm, how much force, in Newtons, will be needed to stretch the same spring by 8cm? The answer is 16.

Last one 27.) A 600-N force is applied to a safe full of gold which weighs 2000 N's but it does not move. What is the friction force exerted by the floor of the safe? answer is 600 N

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[CanadianPre-Med]

I had questions regarding some of the physics problems on the OPTED exam. If anyone can help show me how to get the answer given that would be great! my real OAT is tomorrow!

11.) A small girl applies a horizontal force of 2 Newtons to a 10- Newton box which slides across the floor with a constant speed of 3 m/s. What is the frictional force, in Newtons, by the floor on the box. The answer is 2.

Notice that it says constant speed. Constant speed = 0 acceleration. Hence, there should be no net force. The frictional force is opposing the girl's force and should be equal to one another.

13.) Atmospheric pressure is very nearly 100kPa. A sealed container of air at 1 atmospheric pressure has a door 1 m wide and 2 m high. This door is very hard to open during HIGH pressure days. If the atmospheric pressure on the outside of the contain is just 1 percent greater than on the inside, then what added force in Newtons is required to open the container door? The answer is 2,000.

P = F/A; 1 atm = 1000 Pa; P = 1% of 1000 Pa = 100 Pa; A = 2m^2
F = PA = (1000)(2) = 2000 N

16.) A ball is thrown horizontally at 20 m/s from the top of a building and strikes the level ground 50m from the building. Approximately how many meters high is the roof of the building? The answer is 31 m.

x - x_0 = v_0(t) + 1/2at^2 --> x - x_0 = v_0(t) --> 50 = 20(t) --> t = 5/2 = 2.5

y - y_0 = 1/2at^2 --> y - y_0 = 1/2(-9.8)(2.5^2)= 30.625 ~ 31 m

22.) If an 80-cm long spring requires 10 Newtons to stretch 5 cm, how much force, in Newtons, will be needed to stretch the same spring by 8cm? The answer is 16.

F = kx; 10 = k(0.05) --> k = 200 (K is constant and inherent to the spring)
F = kx; F = (200)(0.08) --> k = 16

Last one 27.) A 600-N force is applied to a safe full of gold which weighs 2000 N's but it does not move. What is the friction force exerted by the floor of the safe? answer is 600 N

Again, since it doesn't accelerate, there is no net force and the opposing forces must equal one another.

Answers above.

 

[thanotoriousfob]

Answers above.

Awesome!! Thanks for the help!