Physics exam 1

Taking up as positive at the highest point the acceleration and vertical velocity of a projectile respectively are

-9.80 and 0

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

20 N left

When the speed of your car is doubled, by what factor does its kinetic energy increase?

4

A ball is thrown straight up. At what point does the ball have the most energy?

At every point of the path the energy is the same

A pilot drops a package from a plane flying horizontally at a constant speed. Neglecting air resistance, when the package hits the ground the horizontal location of the plane will

Be directly above the package

Two balls are thrown off a building with the same speed, one straight up and one at a 45 ∘ angle. Which statement is true if air resistance can be ignored?

Both hit the ground with same speed

Which pulls harder gravitationally, the Earth on the Moon, or the Moon on the Earth? Which accelerates more?

Both the same; the Moon.

When an object moves in uniform circular motion the direction of its acceleration is

Directed toward the center of its circular path

Two small balls, A and B, attract each other gravitationally with a force of magnitude F. If we now double both masses and the separation of the balls, what will now be the magnitude of the attractive force on each one?

F

A block of mass m sits at rest on a rough inclined ramp that makes an angle θ with the horizontal. What must be true about force of static friction f on the block?

F = mgsinθ

A mass m is suspended by a string from the ceiling inside an elevator. The elevator is traveling upward with a constant acceleration. The tension in the string is

Greater than Mg

A car accelerating from rest at 2.0 m/s2 for 5 sec

Has a final speed of 10 m/s

A person pushes a block up an incline at a constant speed. As the block moved up the incline

It's kinetic energy remains the same

A simple pendulum consisting of a bob of mass m is attached to a 1 m length string . What is the speed at bottom?

Mgh = (1/2) mv^2 V^2= sqrt (2)(9.80)(1) V= 4.4 m/s

A satellite in circular orbit around the Earth moves at constant speed. This orbit is maintained by the force of gravity between the Earth and the satellite, yet no work is done on the satellite. How is this possible?

No work is done if the direction of motion is perpendicular to the force.

While driving fast around a sharp right turn you find yourself pressing against the car door . What is happening ?

The door is exerting a rightward force on you.

An object has a mass of 120 kg on earth. What are the mass and weight of this object on the surface of the moon where acceleration due to gravity is 1/6 of earth.

The mass is the same on both planets (120kg) W= (1/6) (9.80) (120) W=196 Newtons

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

The thrown ball ( force is applied to it)

Two objects are thrown from the top of a tall building. One is thrown up, and the other is thrown down, both with the same initial speed. What are their speeds when they hit the street?

They are traveling at the same speed.

Engines are rated in horsepower . This horsepower is the rate at which an engine can do work (T/F)

True

A 100 kg man climbs a 5 m high stair case at a constant speed of 10 s . How much power does he apply?

W= mgh/t W= (100)(9.80)(5.0)/10s W= 490 W

A crate is sliding down an inclined ramp at a constant speed of 0.55 m/s. The vector sum of all the forces acting on this crate must point

Zero

Suppose an object is accelerated by a force of 100 N . Suddenly a second force of 100 N in the opposite direction is exerted on the object so that the forces cancel. The object

continues at the velocity it had before the second force was applied

You push a heavy crate down a ramp at a constant velocity. Only four forces act on the crate. Which force does the greatest magnitude of work on the crate?

force of friction

In the international space station which orbits earth astronauts experience apparent weightlessness because

the astronauts and the station are in free fall towards the center of the Earth.

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

the force you exert on the box is equal to the force of the box pushing back on you