Q: A tractor pulls a sled with a force of 5000 N at an angle of 36.9° above the horizontal for 20 m. What is the work done by the tractor?

$$W = 5000 \times 20 \times \cos 36.9^\circ$$

Q: A friction force of 3500 N opposes the sled's motion for 20 m. What is the work done by friction?

$$W = 3500 \times 20 \times \cos 180^\circ$$

Question 1

Which equation correctly describes the weight $$w of an $$astronaut at a distance $$r$$ from the center of the Earth?

Accepted Answer

$$w = G m_E m / r^2$

Question 2

As altitude increases above the Earth's surface, what happens to the weight of an object?

Accepted Answer

It decreases because gravitational force decreases with distance.

Question 3

A satellite is in a circular orbit around the Earth. Which force provides the centripetal acceleration required to keep it in orbit?

Accepted Answer

The Earth's gravitational force.

Question 4

What is the correct expression for the kinetic energy $$K of an $$object with mass $$m$$ and speed $$v$$?

Accepted Answer

$$K = \frac{1}{2} m v^2$

Question 5

A force $$\vec{F}$$ acts at an angle $$\phi to $$the displacement $$\vec{s}. $$What is the formula for the work $$W$$ done by this force?

Accepted Answer

$$W = F s \cos \phi$$

Question 6

A package of mass $$m$$ slides down a frictionless ramp of height $$h$$ inclined at angle $$\beta. $$What is the total work done by all forces on the package?

Accepted Answer

$$W = m g h$$

Question 7

A weightlifter holds a barbell stationary above his head. What is the work done by the weightlifter on the barbell?

Accepted Answer

Zero work.

Question 8

A weightlifter lowers a barbell to the floor. What type of work do the weightlifter's hands do on the barbell?

Accepted Answer

Negative work.

Question 9

A tractor pulls a sled with a force of 5000 N at an angle of 36.9° above the horizontal for 20 m. What is the work done by the tractor?

Accepted Answer

$$W = 5000 	imes 20 	imes \cos 36.9^\circ$$

Question 10

A friction force of 3500 N opposes the sled's motion for 20 m. What is the work done by friction?

Accepted Answer

$$W = 3500 	imes 20 	imes \cos 180^\circ$$

Question 11

Which scenario results in zero work being done by a force?

Accepted Answer

The force is perpendicular to the displacement.

Question 12

A projectile is launched from point A toward B with increasing initial speed. What happens to its trajectory as the speed increases?

Accepted Answer

It follows a parabolic path and eventually enters orbit.

Question 13

What is the primary method for detecting black holes in binary star systems?

Accepted Answer

Detecting x-rays emitted from the accretion disk.

Question 14

If all the mass of a body lies inside its Schwarzschild radius $$R_s$$, what is the consequence?

Accepted Answer

The body becomes a black hole and no light can escape.

Question 15

Which of the following best describes the direction of acceleration $$\vec{a}$$ for a satellite in a circular orbit?

Accepted Answer

It is always perpendicular to the velocity $$\vec{v}$$ and points toward the center.

Question 16

Which equation represents the scalar (dot) product for work done by a constant force?

Accepted Answer

$$W = \vec{F} \cdot \vec{s}$$

Question 17

In the context of energy conservation, which statement is correct?

Accepted Answer

Energy is conserved; it can be transformed but not created or destroyed.

Question 18

A package slides down a frictionless ramp inclined at angle $$\beta$$ from height $$h. $$What is the expression for the parallel component of weight doing work?

Accepted Answer

$$W = m g h$$

Question 19

A farmer pulls a sled with a force at an angle above the horizontal. Which component of the force does work on the sled?

Accepted Answer

The horizontal component.

Circular Motion, Gravitation, and Work-Energy in Physics

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