Physics Test 1

To convert from ft^2 to yd^2, you should

multiply by 1/9

You are in the middle of a large field. You walk in a straight line for 100 m, then turn left and walk 100 m more in a straight line before stopping. When you stop, you are 100 m from your starting point. By how many degrees did you turn? (a) 90⁰ (b) 120⁰ (c) 30⁰ (d) 180⁰ (e) this is impossible. you cannot walk 200 m and be only 100 m away from where you started.

(b) 120⁰

A car travels 10 m/s east. Another car travels 10 m/s north. The relative speed of the first car with respect to the second is... (a) less than 20 m/s (b) exactly 20 m/s (c) more than 20 m/s

(a) less than 20 m/s the cars are traveling perpendicular to each other, therefore the relative speed is less than the maximum speed that would be equal to 20 m/s and would be reached if the cares were traveling in opposite direction

Which of the following should be part of solving any problem in physics? select all that apply (a) read the problem carefully (b) draw a picture of the situation (c) write down the variables that are given (d) think about which physics principles to apply (e) determine which equations can be used to apply the correct physics principles (f) check the units when you have completed your calculation (g) consider whether your answer is reasonable

(a), (b), (c), (d), (e), (f), and (g)

A satellite is in orbit around the earth. Which object feels the a greater force?

The Earth and the satellite feel exactly the same force

Which statements are NOT valid for a projectile? Take up as positive... (a) the projectile has the same x velocity at any point on its path (b) the acceleration of the projectile is positive and decreasing when the projectile is moving upwards, zero at the top, and increasingly negative as the projectile descends (c) the acceleration of the projectile is a constant negative value (d) the y component of the velocity of the projectile is zero at the highest point of the projectile's path (e) the velocity at the highest point is zero

(b) The acceleration of the projectile is positive and decreasing when the projectile is moving upwards, zero at the top, and increasingly negative as the projectile descends (e) The velocity at the highest point is zero

A ball is thrown downward at a speed of 20 m/s. Choosing the +y axis pointing upward and neglecting air resistance, which equation(s) could be used to solve for other variables? The acceleration due to gravity is g=9.8 m/s² downward. (a) v = (20 m/s) - gt (b) y = yo + (-20 m/s)t - (1/2)gt^2 (c) v^2 = (20 m/s)^2 - 2g(y-yo) (d) (20m/s) = (v+vo)/2 (e) all of the above

(b) and (c) are correct Velocity has to be negative if going upwards in y direction is positive, so a and e are incorrect. the average velocity should not equal the initial velocity so d is incorrect. equations b and c are correctly written along with the signs based on the direction.

The normal force on an extreme skier descending a very steep slope can be zero if... (a) his speed is great enough (b) he leaves the slope (no longer touches the snow) (c) the slope is greater than 75 degreed (d) the slope is vertical (90 degrees)

(b) and (d)

Accuracy represents (a) repeatability of a measurement, using a given instrument (b) how close a measurement is to the true value (c) an ideal number of measurements to make (d) how poorly an instrument is operating

(b) how close a measurement is to the true value

You are adding vectors of length 20 and 40 units. Which of the following choices is a possible resultant magnitude? (a) 0 (b) 18 (c) 37 (d) 64 (e) 100

(c) 37

Suppose an object is accelerated by a force of 100 N. Suddenly a force of 100 N in the opposite direction is exerted on the object, so that the forces cancel. The object... (a) is brought to rest (b) decelerates gradually to rest (c) continues at the velocity it had before the second force was applied (d) is brought to rest and then accelerates in the direction of the second force. If two equal and opposite forced are acting on an object, the net force acting on it is zero. From Newton's first law of motion, the object continues in the state where the net force acting on it is zero. Therefore, the object continues with the velocity at which the second force acted on it.

(c) continues at the velocity that it had before the second force was applied If two equal and opposite forced are acting on an object, the net force acting on it is zero. From Newton's first law of motion, the object continues in the state where the net force acting on it is zero. Therefore, the object continues with the velocity at which the second force acted on it.

A person stands on a scale in an elevator. His apparent weight will be the greatest when the elevator... (a) is standing still (b) is moving upward at a constant velocity (c) is accelerating upward (d) is moving downward at a constant velocity (e) is accelerating downward

(c) is accelerating upward When the elevator is at rest or moving with constant velocity, the net force acting on the elevator is zero, and for a person standing on a scale in the elevator, his weight is equal to the normal force acting on him (mass x gravity). The normal force acting on the person is less than his apparent weight when the elevator is accelerating upward. So, the person has a greater apparent weight.

Which is NOT true about an order-of-magnitude estimation? (a) It can be used to check if an exact calculation is reasonable. (b) It may require making some reasonable assumptions in order to calculate the answer. (c) It will always be accurate to at least two significant figures. (d) It gives you a rough idea of the answer. (e) It can be done by keeping only one significant figure.

(c) it will always be accurate to at least two significant figures

You drive 4 km at 30 km/h and then another 4 km at 50 km/h. What is your average speed for the entire 8 km trip? (a) more than 40 km/h (b) equal to 40 km/h (c) less than 40 km/h (d) not enough information

(c) less than 40 km/h average speed = distance/time elapsed (in hours) = 8km/((4/50)+(4/30)) = 37.5 km/h

To pull an old stump out of the ground, you and a friend tie two ropes to the stump. You pull on it with a force of 500 N to the north while your friend pulls with a force of 450 N to the northwest. The total force from the two ropes is... (a) less than 950 N (b) exactly 950 N (c) more than 950 N

(c) less than 950 N Because the 450 N is applied at a direction that is north west, it will have both north and west components of force. The value of these components of forces will always less than 450 N. Only the north component of force (which is less than 450 N) is added to the force of 500 N, totaling a net force that is less than 950 N.

When a skier skis down a hill, the normal force exerted on the skier by the hill is... (a) equal to the weight of the skier (b) greater than the weight of the skier (c) less than the weight of the skier

(c) less than the weight of the skier The normal force exerted on a skier of mass (m) sliding on a hill is equal to his weight component. Because the hill is at a nonzero angle, the normal force acting on the skier will be equal to mg x cos(theta) which is less than mg, so the normal force will be less than the weight of the skier (mg)

In which of the following cases does a car have a negative velocity and a positive acceleration? (a) - x direction at a constant 20 m/s (b) - x direction increasing in speed (c) + x direction increasing in speed (d) - x direction decreasing in speed (e) + x direction decreasing in speed

(d) -x direction decreasing in speed

[L^2] represents the dimensions for which of the following? (a) cm^2 (b) ft^2 (c) m^2 (d) all of the above

(d) all of the above the dimensional formula [L^2] represents a physics quantity called area, which is square of a length. So anything that can be used as units for area is the correct answer.

A student weighs herself on a digital bathroom scale as 117.4 lbs. If all the digits displayed reflect the true precision of the scale, then probably her weight is (a) within 1% of 117.4 lb. (b) exactly 117.4 lb. (c) somewhere between 117.38 and 117.42 lb. (d) somewhere between 117.2 and 117.6 lb.

(d) somewhere between 117.2 and 117.6 lbs

At time t=o an object is traveling to the right along the +x axis at a speed of 10 m/s with acceleration -2 m/s². Which statement is true? (a) the object will slow down, eventually coming to a complete stop (b) the object cannot have a negative acceleration and be moving to the right (c) the object will continue to move to the right, slowing down but never coming to a complete stop (d) the object will slow down, momentarily stopping, then pick up speed moving to the left

(d) the object will slow down, momentarily stopping, then pick up speed moving to the left

Four students use different instruments to measure the length of the same one. Which measurement implies greatest precision? (a) 160.0mm. (b) 16.0 cm. (c) 0.160 m. (d) 0.00016 km. (e) Need more information.

160.0 mm (because it has the greatest number of significant figures)

The number 0.0078 has how many significant figures?

2

A 50-N crate sits on a horizontal floor where the coefficient of static friction between the floor is 0.50. A 20-N force is applied to the crate acting to the right. What is the resulting static friction force acting on the crate?

20 N to the left

How many significant figures does 1.362 + 25.2 have?

3

You drop a rock off a bridge. When the rock has fallen 4 m, you drop a second rock. As the two rocks continue to fall, what happens to their velocities?

Both increase at the same rate

You are riding in an enclosed train car at 90 km/h. If you throw a baseball straight up, where will the baseball land?

In your hand If the horizontal component of velocity remains constant then the ball would cover the same horizontal distance as you do, and will therefore come back directly into your hand.

A ball is thrown straight up, reaches a maximum height, then falls to its initial height. Which of the following statements about the direction of the velocity and acceleration of the ball as it is going up is correct?

Its velocity points upward and its acceleration points downward.

A truck is traveling horizontally to the right. When the truck starts to slow down, the crate on the truck bed starts to slide. In what direction could the net force be on the crate?

No direction. The net force is zero. newton's first law states that every object continues in its state of rest, or of uniform velocity as long as no net force is acting on it. Because the truck bed is a frictionless surface, and there is not force to move the crate, the crate maintains its velocity and slides.

A ball is dropped from the top of a tall building. At the same instant, another ball is thrown upward from the ground level. When the two balls pass one another, one on the way up, one on the way down, compare the magnitudes of their acceleration.

The acceleration of both balls is the same

A hunter is aiming horizontally at a monkey who is sitting in a tree. The monkey is so terrified when it sees the gun that it falls from the tree. At that very instant, the hunter pulls the trigger. What will happen?

The bullet will hit the monkey because both the monkey and the bullet are falling downward at the same rate due to gravity

One ball is dropped vertically from a window. At the same time, a second ball is thrown horizontally from the same window. Which ball has the greater speed at ground level?

The thrown ball The horizontal component of acceleration of the thrown ball provides extra velocity.

A baseball player hits a ball that soars high into the air. After the ball has left the bat, and while it is traveling upward, what is the direction of acceleration? Ignore air resistance...

downward direction

A bullet fired from a rifle begins to fall...

as soon as it leaves the barrel

A car travels along the x-axis with increasing speed. We don't know to the left or to the right. Which of the graphs most closely represents the motion of the car?

concave down

A 10-kg rock and a 20-kg rock are thrown upward with the same initial speed (Vo) and experience no significant air resistance. If the 10-kg rock reaches a maximum height h, what maximum height will the 20-kg ball reach?

h (because max height is not mass dependent)

A bear sling is used in some national parks for placing backpackers' food out of the reach of bears. As the backpacker raises the pack by pulling down on the rope, the force F needed...

increases, but the rope always sags where the pack hangs

For general projectile motion with no air resistance, the horizontal component of a projectile's acceleration

is always zero

An object moving in the +x direction experiences an acceleration of 2.0 m/s^2. This means the object

is increasing its velocity by 2.0 m/s every second

The magnitude of a component of a vector must be...

less than or equal to the magnitude of the vector

A golf ball is hit with a golf club. While the ball flies through the air, which forces act on the ball? Neglect air resistance...

the force of gravity acting on the ball

What causes the boat in the picture to move forward?

the force that the water exerts on the paddle the acceleration of the boat in the forward direction is due to the horizontal forces acting on the boat. The man exerts a force on the paddle of the boat to push the water backwards. An equal and opposite force is exerted by the water on the paddles, which must be what makes the boat move forward

You are pushing a heavy box across a rough floor. When you are initially pushing the box and it is accelerating...

the force that you exert on the box is equal to the force of the box pushing back on you The box applies the frictional force in the opposite direction of the force that the person applies when pushing the box the box will accelerate when both forces applied by the person and the frictional force applied by the person is balanced according to newton's third law, the force exerted by the person will be equal to the force exerted by the box on the person.

You are trying to push your stalled car. Although you apply a horizontal force of 400 N to the car, it doesn't budge, and neither do you. Which force(s) must also have a magnitude of 400 N?

the friction force exerted by the road on you

In the picture, Matt is able to move the truck because...

the ground exerts a greater friction force on Matt than it does on the truck for the truck to move forward, the force exerted on the truck by the person must be greater than the frictional force exerted by the ground on the truck/ The force exerted by the person on the truck is greater because of the greater frictional force exerted by the ground on the person. This frictional force exerted by the ground on the person is more when compared to the frictional force exerted by the ground on the truck, allowing the person to move the truck forward.

A baseball is hit high and far. Which of the following statements is true? At the highest point...

the magnitude of the velocity is the slowest

Which of the three kicks in the figure is in the air for the longest amount of time? They all reach the same maximum height, h. Ignore air resistance...

they are all the same Because the vertical component of velocity and the maximum height reached by all three of the balls are the same, the time of flight for all the balls is the same because they all remain in the air for the same amount of time. The distances covered by the balls are different because the different angles of inclinations provides different horizontal components to the ball.

A ball is thrown straight up. What are the velocity and acceleration of the ball at the highest point in its path?

v=0, a=9.8 m/s² down