Physics 4-7

A 615N student standing on a scale in an elevator notice that the scale reads 645N the student knows that the elevator is moving

you cannot tell if it is moving upward or downward

A stalled car is being pushed up a hill with a constant velocity by three people. The net force of the car is...

zero

A string is attached to the rear-view mirror of a car. A ball is hanging at the other end of the string. The car is driving around in a circle, at a constant speed. Which of the following lists gives all of the forces directly acting on the ball?

Tension and Gravity

A stock person at the local grocery store has a job consisting of the following five segments: (1) picking up boxes of tomatoes from the stockroom floor (2) accelerating to a comfortable speed (3) carrying the boxes to the tomato display at constant speed (4) decelerating to a stop (5) lowering the boxes slowly to the floor. During which of the five segments of the job does the stock person do positive work on the boxes?

1 and 2

Which, if any, of the following three statements concerning the work done by a conservative force is NOT true? Select option "All of the above statements are true." if all three statements are true. It is independent of the path of the body and depends only on the starting and ending points. It can always be expressed as the difference between the initial and final values of a potential energy function.

All of the above statements are true

Two stones, one of mass m and the other of mass 2m, are thrown directly upward with the same velocity at the same time from ground level and feel no air resistance. Which statement about these stones is true?

At its highest point, the heavier stone will have twice as much gravitational potential energy as the lighter one because it is twice as heavy.

Two identical balls are thrown directly upward, ball A at speed v and ball B at speed 2v, and they feel no air resistance. Which statement about these balls is correct?

Ball B will go four times as high as ball A because it had four times the initial kinetic energy.

Block 1 and block 2 have the same mass, m, and are released from the top of two inclined planes of the same height making 30° and 60° angles with the horizontal direction, respectively. If the coefficient of friction is the same in both cases, which of the blocks is going faster when it reaches the bottom of its respective incline?

Block two is faster

Is it possible for a system to have negative potential energy?

Yes, since the choice of the zero of potential energy is arbitrary.

You are seated on a bus and notice that a hand strap that is hanging from the ceiling hangs away from the vertical in the backward direction. From this observation, you can conclude that..

You cannot conclude anything about the direction of the velocity of the bus.

A 4.0-kg object is moving with speed 2.0 m/s. A 1.0-kg object is moving with speed 4.0 m/s. Both objects encounter the same constant braking force, and are brought to rest. Which object travels the greater distance before stopping?

Both objects travel the same distance.

Point P in the figure indicates the position of the object travelling at a constant speed clockwise around the circle. Which arrow best represents the direction the object would travel if the net external force on it were suddenly reduced to zero

Down arrow

If you swing a bucket of water fast enough in a vertical circle, at the highest point the water does not spill out because an outward force balances the pull of gravity on the water.

False

A brick is resting on a rough incline as shown in the figure. The friction force acting on the brick, along the incline, is

Less than the weight of the brick

Two men, Joel and Jerry, push against a wall. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do.

Neither of them does any work

A woman is straining to lift a large crate, without success because it is too heavy. We denote the forces on the crate as follows: P is the upward force the woman exerts on the crate, C is the vertical contact force exerted on the crate by the floor, and W is the weight of the crate. How are the magnitudes of these forces related while the woman is trying unsuccessfully to lift the crate?

P+C=W

Two objects masses m1, and m2 are connected to each other shown in the figure are released from the rest. There's no friction on the table surface or in the pulley. The masses of the pulley and the string connecting the objects are negligible. What must be true about the tension T in the string just after the objects are released?

T<m2G

A box of mass m is pulled with a constant acceleration along a horizontal frictionless floor by a wire that makes an angle 15 above the horizontal. If T is the tension in wire, then...

T>ma

An object is moving forward with constant velocity. Which statement of the object MUST be true?

The net force on the object is zero.

A girl throws a stone from a bridge. Consider the following ways she might throw the stone. The speed of the stone as it leaves her hand is the same in each case, and air resistance is negligible. Case A: Thrown straight up. Case B: Thrown straight down. Case C: Thrown out at an angle of 45° above horizontal. Case D: Thrown straight out horizontally. In which case will the speed of the stone be greatest when it hits the water below?

The speed will be the same in all cases

Two objects have the masses m and 5m, respectively. They both are placed side by side on a frictionless inclined plane and allowed to slide down from the rest.

The two objects reach the bottom of the incline at the same zero.

Three cars (car F, car G, and car H) are moving with the same velocity when the driver suddenly slams on the brakes, locking the wheels. The most massive car is car F, the least massive is car H, and all three cars have identical tires. (a) Which car travels the longest distance to skid to a stop? b) For which car does friction do the largest amount of work in stopping the car?

They travel at them same speed Car F

If a force always acts perpendicular to an object's direction of motion, that force cannot change the object's kinetic energy.

True

When an object is solely under the influence of conservative forces, the sum of its kinetic and potential energies does not change.

True

You swing a bat and hit a heavy box with a force of 1500 N. The Force the box exerts on the bat is...

exactly 1500N whether or not the box moves

Two bodies, points P and Q on a smooth horizontal surface are connected by a light cord. The masses of P is greater than Q's. A horizontal force F (of magnitude of F) is applied to Q as shown in the figure, accelerating the bodies to the right. The magnitude of the force exerted by the connecting cord on body P will be

less than F by not zero

Suppose you are playing hockey on a new-age ice surface for which no friction between the ice and hockey puck. You wind up and hit the puck as hard as you can After the puck loses contact with you stick, the puck will...

not slow down and speed up

Suppose the force of the air drag on an object is proportional to the speed of the object and in the direction opposite the object's velocity. If you throw an object upward, the magnitude of its acceleration is greatest

right after the object is released

When a parachutist jumps from an airplane, he eventually reaches a constant speed, called the terminal speed. Once he has reached terminal speed

the force of the air drags on him equal to his weight

Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. When they hit the ground

the heavier one will have twice the kinetic energy of the lighter one.

Consider a plot of the displacement (x) as a function of the applied force (F) for an ideal elastic spring. The slope of the curve would be

the reciprocal of the spring constant.

A ball tossed vertically upward when it reaches its highest point (before falling back downward):

the velocity is zero, the acceleration is directed downward, and the force of gravity acting on the ball is directed downward

A 3.00-kg ball swings rapidly in a complete vertical circle of radius 2.00 m by a light string that is fixed at one end. The ball moves so fast that the string is always taut and perpendicular to the velocity of the ball. As the ball swings from its lowest point to its highest point

the work done on it by gravity is -118 J and the work done on it by the tension in the string is zero.

Swimmers at a water park have a choice of two frictionless water slides as shown in the figure. Although both slides drop over the same height, h, slide 1 is straight while slide 2 is curved, dropping quickly at first and then leveling out. How does the speed v1 of a swimmer reaching the end of slide 1 compares with v2, the speed of a swimmer reaching the end of slide 2?

v1=v2