# Physics Homework Help Please -- block pressed against a wall is sliding...

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Hey! I've been trying to figure out these two problems but can't seem to get the right answer. Was wondering if someone could help me out?

1.

A block is pressed against a vertical wall by a force F, as the drawing shows.

This force can either push the block upward at a constant velocity or allow it to slide downward at a constant velocity. The magnitude of the force is different in the two cases, while the directional angle θ is the same. Kinetic friction exists between the block and the wall, and the coefficient of kinetic friction is 0.260. The weight of the block is 49.0 N, and the directional angle for the force F is θ = 37.0°. Determine the magnitude of Fwhen the block slides (a) up the wall and (b) down the wall.

I got a) and the answer is 76.3N. Can't seem to get b) right though!

2. A penguin slides at a constant velocity of 1.61 m/s down an icy incline. The incline slopes above the horizontal at an angle of 9.48°. At the bottom of the incline, the penguin slides onto a horizontal patch of ice. The coefficient of kinetic friction between the penguin and the ice is the same for the incline as for the horizontal patch. How much time is required for the penguin to slide to a halt after entering the horizontal patch of ice?

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PeterDonis
Mentor
Hi @sophia026 and welcome to PF!

Homework posts should use the homework template; in addition to the problem description, this requires you to post any equations that apply to the problem, and your attempt at a solution. We will be much better able to help you if you provide this additional information.

berkeman
Mentor
Hey! I've been trying to figure out these two problems but can't seem to get the right answer. Was wondering if someone could help me out?

1.

A block is pressed against a vertical wall by a force F, as the drawing shows.
View attachment 231566
This force can either push the block upward at a constant velocity or allow it to slide downward at a constant velocity. The magnitude of the force is different in the two cases, while the directional angle θ is the same. Kinetic friction exists between the block and the wall, and the coefficient of kinetic friction is 0.260. The weight of the block is 49.0 N, and the directional angle for the force F is θ = 37.0°. Determine the magnitude of Fwhen the block slides (a) up the wall and (b) down the wall.

I got a) and the answer is 76.3N. Can't seem to get b) right though!

2. A penguin slides at a constant velocity of 1.61 m/s down an icy incline. The incline slopes above the horizontal at an angle of 9.48°. At the bottom of the incline, the penguin slides onto a horizontal patch of ice. The coefficient of kinetic friction between the penguin and the ice is the same for the incline as for the horizontal patch. How much time is required for the penguin to slide to a halt after entering the horizontal patch of ice?
Welcome to the PF.

haruspex
Homework Helper
Gold Member
... and please post each unrelated question as a separate thread, with a title that gives some indication of the subject matter.

gneill and Chestermiller
For Que. 1b, I suggest you draw Free-Body Diagram for the system by taking kinetic friction in the upward direction and then apply Newton's Laws of Motion as you might have done for solving Que. 1a. It's just the matter of directions and algebra and you'll get the answer.

<< Mentor Note -- post edited to remove solution >>

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