Q: A block of mass $$m is $$pulled with force $$F at an $$angle $$\theta$$ above the horizontal on a frictionless surface. What is the acceleration of the block?

$$a = \frac{F \cos \theta}{m}$$

Question 1

A skier pushes off the ground to start moving forward, as shown in the image. According to Newton’s 3rd law, what is the direction of the force exerted by the ground on the skier?

Accepted Answer

Forward, in the same direction as the skier's motion

Question 2

A block of mass $$m is $$placed on an inclined plane with angle $$	heta. $$The coefficient of static friction is $$\mu_s. At $$what minimum angle $$	heta$$ will the block start to slide?

Accepted Answer

$$	heta = \arctan(\mu_s)$$

Question 3

A person carries a heavy stone horizontally across a field at constant speed. According to the physics definition of work, how much work does the person do against gravity?

Accepted Answer

Zero work

Question 4

A rifle of mass $$M$$ fires a bullet of mass $$m$$ with velocity $$v_b. $$What is the recoil velocity $$v_r of $$the rifle?

Accepted Answer

$$v_r = -\frac{m}{M} v_b$$

Question 5

A block slides down a frictionless incline of height $$h. $$What is its speed at the bottom?

Accepted Answer

$$v = \sqrt{2gh}$$

Question 6

A car of mass $$m$$ traveling at speed $$v_0$$ comes to a stop due to friction with coefficient $$\mu_k. $$What is the stopping distance $$\Delta x$$?

Accepted Answer

$$\Delta x = \frac{v_0$^2}{2\mu_k g}$$

Question 7

A spring with constant $$k is $$compressed by $$x. $$What is the potential energy stored in the spring?

Accepted Answer

$$U = \frac{1}{2}kx^2$

Question 8

A bow (modeled as a spring with constant $$k) is $$pulled back a distance $$x$$ and used to shoot an arrow of mass $$m. $$What is the initial velocity $$v of $$the arrow?

Accepted Answer

$$v = \sqrt{\frac{k}{m}} x$$

Question 9

If an archer shoots six arrows at once using the same bow, how does the distance each arrow travels compare to shooting a single arrow?

Accepted Answer

Each arrow travels 1/6 the distance of a single arrow

Question 10

A block of mass $$m is $$pulled across a rough surface with friction force $$f_k$$ over a distance $$\Delta x. If $$the applied force is $$F at $$angle $$\phi to $$the horizontal, what is the net work done on the block?

Accepted Answer

$$W = F \cos \phi \Delta x - f_k \Delta x$$

Question 11

A ball of mass $$m$$ moving at velocity $$v$$ collides elastically with a stationary wall. What is the velocity of the ball after the collision?

Accepted Answer

$$-v ($$opposite direction)

Question 12

In a perfectly inelastic collision, two objects stick together after colliding. What fraction of the initial kinetic energy is lost if both objects have equal mass?

Accepted Answer

1/2

Question 13

A roller coaster starts at rest at height $$h_1$$ and descends to height $$h_2 ($$neglecting friction). What is its speed at $$h_2$$?

Accepted Answer

$$v = \sqrt{2g(h_1$ - h_2$)}$$

Question 14

A horse pulls a cart on level ground. According to Newton’s 3rd law, what is the force that actually moves the horse and cart forward?

Accepted Answer

The force of the ground on the horse

Question 15

A block of mass $$m$$ slides down a frictionless ramp of height $$h$$ and then compresses a spring with constant $$k. $$What is the maximum compression $$x of $$the spring?

Accepted Answer

$$x = \sqrt{\frac{2mgh}{k}}$$

Question 16

A person throws a ball while standing on a cart. The ball bounces off a screen attached to the cart. What is the final direction of the cart’s motion?

Accepted Answer

It moves in the direction opposite to the ball's final motion

Question 17

A skier leans into a turn, pushing against the snow. Which force allows the skier to change direction?

Accepted Answer

Friction force from the snow

Question 18

A block of mass $$m is $$pulled with force $$F at an $$angle $$	heta$$ above the horizontal on a frictionless surface. What is the acceleration of the block?

Accepted Answer

$$a = \frac{F \cos 	heta}{m}$$

Question 19

A ball is thrown vertically upward. At the highest point, which of the following is true?

Accepted Answer

Potential energy is maximum

Physics 211: Forces, Motion, Work, Energy, and Momentum – Comprehensive Study Notes

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